[benchmark] Move build configuration/sdk configuration out of the main CMakeLists.txt file into AddSwiftBenchmarkSuite.cmake.

I am going to add some support here for Linux. I want to make sure that these
changes are hidden from the main CMakeLists.txt file since we want that file to
be as declarative as possible.

rdar://40541972

benchmark/cmake/modules/AddSwiftBenchmarkSuite.cmake

@@ -2,6 +2,70 @@
 include(CMakeParseArguments)
 include(SwiftBenchmarkUtils)
 
+macro (configure_build)
+  add_definitions(-DSWIFT_EXEC -DSWIFT_LIBRARY_PATH -DONLY_PLATFORMS
+                  -DSWIFT_OPTIMIZATION_LEVELS -DSWIFT_BENCHMARK_EMIT_SIB)
+
+  if(NOT ONLY_PLATFORMS)
+    set(ONLY_PLATFORMS "macosx" "iphoneos" "appletvos" "watchos")
+  endif()
+
+  if(NOT SWIFT_EXEC)
+    runcmd(COMMAND "xcrun" "-f" "swiftc"
+           VARIABLE SWIFT_EXEC
+           ERROR "Unable to find Swift driver")
+  endif()
+
+  if(NOT SWIFT_LIBRARY_PATH)
+    get_filename_component(tmp_dir "${SWIFT_EXEC}" DIRECTORY)
+    get_filename_component(tmp_dir "${tmp_dir}" DIRECTORY)
+    set(SWIFT_LIBRARY_PATH "${tmp_dir}/lib/swift")
+  endif()
+
+  # If the CMAKE_C_COMPILER is already clang, don't find it again,
+  # thus allowing the --host-cc build-script argument to work here.
+  get_filename_component(c_compiler ${CMAKE_C_COMPILER} NAME)
+
+  if(${c_compiler} STREQUAL "clang")
+    set(CLANG_EXEC ${CMAKE_C_COMPILER})
+  else()
+    runcmd(COMMAND "xcrun" "-toolchain" "${SWIFT_DARWIN_XCRUN_TOOLCHAIN}" "-f" "clang"
+           VARIABLE CLANG_EXEC
+           ERROR "Unable to find Clang driver")
+  endif()
+endmacro()
+
+macro (configure_sdks)
+  set(macosx_arch "x86_64")
+  set(iphoneos_arch "arm64" "armv7")
+  set(appletvos_arch "arm64")
+  set(watchos_arch "armv7k")
+
+  set(macosx_ver "10.9")
+  set(iphoneos_ver "8.0")
+  set(appletvos_ver "9.1")
+  set(watchos_ver "2.0")
+
+  set(macosx_triple_platform "macosx")
+  set(iphoneos_triple_platform "ios")
+  set(appletvos_triple_platform "tvos")
+  set(watchos_triple_platform "watchos")
+
+  set(sdks)
+  set(platforms)
+  foreach(platform ${ONLY_PLATFORMS})
+    execute_process(
+        COMMAND "xcrun" "--sdk" "${platform}" "--show-sdk-path"
+        OUTPUT_VARIABLE ${platform}_sdk
+        RESULT_VARIABLE result
+        ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
+    if("${result}" MATCHES "0")
+      list(APPEND sdks "${${platform}_sdk}")
+      list(APPEND platforms ${platform})
+    endif()
+  endforeach()
+endmacro()
+
 function (add_swift_benchmark_library objfile_out sibfile_out)
   cmake_parse_arguments(BENCHLIB "" "MODULE_PATH;SOURCE_DIR;OBJECT_DIR" "SOURCES;LIBRARY_FLAGS;DEPENDS" ${ARGN})