[wasm][build] Add WASILibc module and its build support

[wasi-libc](https://github.com/WebAssembly/wasi-libc) is a libc
implementation widely used in WASI toolchains. This patch adds a new
module named WASILibc. Some extra emulation libraries are also added as
wasi_emulated_xxx.

stdlib/public/Platform/CMakeLists.txt

@@ -114,6 +114,23 @@ add_swift_target_library(swiftMusl ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_SDK_OV
     TARGET_SDKS MUSL
     INSTALL_IN_COMPONENT sdk-overlay)
 
+add_swift_target_library(swiftWASILibc ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_SDK_OVERLAY
+    ${swift_platform_sources}
+    POSIXError.swift
+
+    GYB_SOURCES
+      ${swift_platform_gyb_sources}
+      WASILibc.swift.gyb
+
+    SWIFT_COMPILE_FLAGS
+      ${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS}
+      ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
+      ${swift_platform_compile_flags}
+    LINK_FLAGS "${SWIFT_RUNTIME_SWIFT_LINK_FLAGS}"
+    TARGET_SDKS WASI
+    INSTALL_IN_COMPONENT sdk-overlay
+    DEPENDS wasilibc_modulemap)
+
 add_swift_target_library(swiftCRT ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_SDK_OVERLAY
     ucrt.swift
     ${swift_platform_sources}
@@ -234,6 +251,43 @@ add_custom_target(glibc_modulemap DEPENDS ${glibc_modulemap_target_list})
 set_property(TARGET glibc_modulemap PROPERTY FOLDER "Miscellaneous")
 add_dependencies(sdk-overlay glibc_modulemap)
 
+set(wasilibc_modulemap_target_list)
+if("WASI" IN_LIST SWIFT_SDKS)
+  set(wasilibc_modulemap_source "wasi-libc.modulemap")
+  foreach(arch ${SWIFT_SDK_WASI_ARCHITECTURES})
+    set(arch_subdir "${SWIFT_SDK_WASI_LIB_SUBDIR}/${arch}")
+    set(module_dir "${SWIFTLIB_DIR}/${arch_subdir}")
+    set(module_dir_static "${SWIFTSTATICLIB_DIR}/${arch_subdir}")
+
+    add_custom_command_target(
+      copy_wasilibc_modulemap_resource
+      COMMAND
+        "${CMAKE_COMMAND}" "-E" "make_directory" ${module_dir} ${module_dir_static}
+      COMMAND
+        "${CMAKE_COMMAND}" "-E" "copy_if_different"
+          "${CMAKE_CURRENT_SOURCE_DIR}/${wasilibc_modulemap_source}" ${module_dir}
+      COMMAND
+        "${CMAKE_COMMAND}" "-E" "copy_if_different"
+          "${CMAKE_CURRENT_SOURCE_DIR}/${wasilibc_modulemap_source}" ${module_dir_static}
+      OUTPUT ${module_dir}/${wasilibc_modulemap_source} ${module_dir_static}/${wasilibc_modulemap_source}
+      COMMENT "Copying WASILibc modulemap to resource directories")
+    add_dependencies(sdk-overlay ${copy_wasilibc_modulemap_resource})
+    list(APPEND wasilibc_modulemap_target_list ${copy_wasilibc_modulemap_resource})
+
+    swift_install_in_component(FILES "${wasilibc_modulemap_source}"
+                               DESTINATION "lib/swift/${arch_subdir}"
+                               COMPONENT sdk-overlay)
+    if(SWIFT_BUILD_STATIC_STDLIB)
+      swift_install_in_component(FILES "${wasilibc_modulemap_source}"
+                                 DESTINATION "lib/swift_static/${arch_subdir}"
+                                 COMPONENT sdk-overlay)
+    endif()
+  endforeach()
+endif()
+add_custom_target(wasilibc_modulemap DEPENDS ${wasilibc_modulemap_target_list})
+set_property(TARGET wasilibc_modulemap PROPERTY FOLDER "Miscellaneous")
+add_dependencies(sdk-overlay wasilibc_modulemap)
+
 if(WINDOWS IN_LIST SWIFT_SDKS)
   swift_install_in_component(FILES
       ucrt.modulemap

stdlib/public/Platform/WASILibc.swift.gyb

@@ -0,0 +1,159 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+@_exported import SwiftWASILibc // Clang module
+
+//  Constants defined by <math.h>
+@available(swift, deprecated: 3.0, message: "Please use 'Double.pi' or '.pi' to get the value of correct type and avoid casting.")
+public let M_PI = Double.pi
+
+@available(swift, deprecated: 3.0, message: "Please use 'Double.pi / 2' or '.pi / 2' to get the value of correct type and avoid casting.")
+public let M_PI_2 = Double.pi / 2
+
+@available(swift, deprecated: 3.0, message: "Please use 'Double.pi / 4' or '.pi / 4' to get the value of correct type and avoid casting.")
+public let M_PI_4 = Double.pi / 4
+
+@available(swift, deprecated: 3.0, message: "Please use '2.squareRoot()'.")
+public let M_SQRT2 = 2.squareRoot()
+
+@available(swift, deprecated: 3.0, message: "Please use '0.5.squareRoot()'.")
+public let M_SQRT1_2 = 0.5.squareRoot()
+
+//  Constants defined by <float.h>
+@available(swift, deprecated: 3.0, message: "Please use 'T.radix' to get the radix of a FloatingPoint type 'T'.")
+public let FLT_RADIX = Double.radix
+
+%for type, prefix in [('Float', 'FLT'), ('Double', 'DBL')]:
+//  Where does the 1 come from? C counts the usually-implicit leading
+//  significand bit, but Swift does not. Neither is really right or wrong.
+@available(swift, deprecated: 3.0, message: "Please use '${type}.significandBitCount + 1'.")
+public let ${prefix}_MANT_DIG = ${type}.significandBitCount + 1
+
+//  Where does the 1 come from? C models floating-point numbers as having a
+//  significand in [0.5, 1), but Swift (following IEEE 754) considers the
+//  significand to be in [1, 2). This rationale applies to ${prefix}_MIN_EXP
+//  as well.
+@available(swift, deprecated: 3.0, message: "Please use '${type}.greatestFiniteMagnitude.exponent + 1'.")
+public let ${prefix}_MAX_EXP = ${type}.greatestFiniteMagnitude.exponent + 1
+
+@available(swift, deprecated: 3.0, message: "Please use '${type}.leastNormalMagnitude.exponent + 1'.")
+public let ${prefix}_MIN_EXP = ${type}.leastNormalMagnitude.exponent + 1
+
+@available(swift, deprecated: 3.0, message: "Please use '${type}.greatestFiniteMagnitude' or '.greatestFiniteMagnitude'.")
+public let ${prefix}_MAX = ${type}.greatestFiniteMagnitude
+
+@available(swift, deprecated: 3.0, message: "Please use '${type}.ulpOfOne' or '.ulpOfOne'.")
+public let ${prefix}_EPSILON = ${type}.ulpOfOne
+
+@available(swift, deprecated: 3.0, message: "Please use '${type}.leastNormalMagnitude' or '.leastNormalMagnitude'.")
+public let ${prefix}_MIN = ${type}.leastNormalMagnitude
+
+@available(swift, deprecated: 3.0, message: "Please use '${type}.leastNonzeroMagnitude' or '.leastNonzeroMagnitude'.")
+public let ${prefix}_TRUE_MIN = ${type}.leastNonzeroMagnitude
+
+%end
+
+public let MAP_FAILED: UnsafeMutableRawPointer! = UnsafeMutableRawPointer(bitPattern: -1)
+
+// NOTE: wasi-libc's error.h defines these macros as function-like macros, which ClangImporter can't import for now.
+%{
+posix_error_codes = [
+  "E2BIG",
+  "EACCES",
+  "EADDRINUSE",
+  "EADDRNOTAVAIL",
+  "EAFNOSUPPORT",
+  "EAGAIN",
+  "EALREADY",
+  "EBADF",
+  "EBADMSG",
+  "EBUSY",
+  "ECANCELED",
+  "ECHILD",
+  "ECONNABORTED",
+  "ECONNREFUSED",
+  "ECONNRESET",
+  "EDEADLK",
+  "EDESTADDRREQ",
+  "EDOM",
+  "EDQUOT",
+  "EEXIST",
+  "EFAULT",
+  "EFBIG",
+  "EHOSTUNREACH",
+  "EIDRM",
+  "EILSEQ",
+  "EINPROGRESS",
+  "EINTR",
+  "EINVAL",
+  "EIO",
+  "EISCONN",
+  "EISDIR",
+  "ELOOP",
+  "EMFILE",
+  "EMLINK",
+  "EMSGSIZE",
+  "EMULTIHOP",
+  "ENAMETOOLONG",
+  "ENETDOWN",
+  "ENETRESET",
+  "ENETUNREACH",
+  "ENFILE",
+  "ENOBUFS",
+  "ENODEV",
+  "ENOENT",
+  "ENOEXEC",
+  "ENOLCK",
+  "ENOLINK",
+  "ENOMEM",
+  "ENOMSG",
+  "ENOPROTOOPT",
+  "ENOSPC",
+  "ENOSYS",
+  "ENOTCONN",
+  "ENOTDIR",
+  "ENOTEMPTY",
+  "ENOTRECOVERABLE",
+  "ENOTSOCK",
+  "ENOTSUP",
+  "ENOTTY",
+  "ENXIO",
+  "EOVERFLOW",
+  "EOWNERDEAD",
+  "EPERM",
+  "EPIPE",
+  "EPROTO",
+  "EPROTONOSUPPORT",
+  "EPROTOTYPE",
+  "ERANGE",
+  "EROFS",
+  "ESPIPE",
+  "ESRCH",
+  "ESTALE",
+  "ETIMEDOUT",
+  "ETXTBSY",
+  "EXDEV",
+  "ENOTCAPABLE",
+]
+}%
+
+%for ecode in posix_error_codes:
+
+public let ${ecode} = POSIXErrorCode.${ecode}.rawValue
+
+%end
+
+// NOTE: wasi-libc's _seek.h defines these macros as function-like macros, which ClangImporter can't import for now.
+
+public let SEEK_SET: Int32 = 0
+public let SEEK_CUR: Int32 = 1
+public let SEEK_END: Int32 = 2

stdlib/public/Platform/wasi-libc.modulemap

@@ -0,0 +1,98 @@
+//===--- wasi-libc.modulemap.gyb ------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+module SwiftWASILibc [system] {
+  header "stdc-predef.h"
+  header "features.h"
+
+  // C standard library
+  header "complex.h"
+  header "ctype.h"
+  header "errno.h"
+  header "fenv.h"
+  header "float.h"
+  header "inttypes.h"
+  header "iso646.h"
+  header "limits.h"
+  header "locale.h"
+  header "math.h"
+  header "stdarg.h"
+  header "stdbool.h"
+  header "stddef.h"
+  header "stdint.h"
+  header "stdio.h"
+  header "stdlib.h"
+  header "string.h"
+  header "tgmath.h"
+  header "time.h"
+
+  // POSIX
+  header "arpa/inet.h"
+  header "cpio.h"
+  header "dirent.h"
+  header "fcntl.h"
+  header "fmtmsg.h"
+  header "fnmatch.h"
+  header "ftw.h"
+  header "glob.h"
+  header "iconv.h"
+  header "ifaddrs.h"
+  header "langinfo.h"
+  header "libgen.h"
+  header "monetary.h"
+  header "netinet/in.h"
+  header "netinet/tcp.h"
+  header "nl_types.h"
+  header "poll.h"
+  header "regex.h"
+  header "sched.h"
+  header "search.h"
+  header "semaphore.h"
+  header "strings.h"
+  header "sys/file.h"
+  header "sys/ioctl.h"
+  header "sys/select.h"
+  header "sys/socket.h"
+  header "sys/stat.h"
+  header "sys/time.h"
+  header "sys/types.h"
+  header "sys/uio.h"
+  header "sys/un.h"
+  header "sys/utsname.h"
+  header "sysexits.h"
+  header "tar.h"
+  header "unistd.h"
+  header "utime.h"
+
+  // WASI specific
+  header "wasi/api.h"
+  export *
+}
+
+module wasi_emulated_mman {
+  header "sys/mman.h"
+  link "wasi-emulated-mman"
+  export *
+}
+
+module wasi_emulated_process_clock {
+  header "sys/times.h"
+  header "sys/resource.h"
+  link "wasi-emulated-process-clocks"
+  export *
+}
+
+module wasi_emulated_signal {
+  header "signal.h"
+  link "wasi-emulated-signal"
+  export *
+}