Fix the clang dependency of sourcekit libraries.

Because swift_swap_compiler_if_needed updates the compiler ID to
Clang, we need to account for it when deciding to add a dependency on
clang. Otherwise, the sourcekit build could fail due to the clang
executable not having been built there yet.

cmake/modules/SwiftWindowsSupport.cmake

@@ -104,6 +104,7 @@ macro(swift_swap_compiler_if_needed target)
       endif()
       set(CMAKE_C_COMPILER_ID Clang)
       set(CMAKE_CXX_COMPILER_ID Clang)
+      set(SOURCEKIT_SWIFT_SWAP_COMPILER TRUE)
       message(STATUS "C/C++ compiler for ${target} is set to: ${CMAKE_C_COMPILER}")
     else()
       message(SEND_ERROR "${target} requires a clang based compiler. Please set SWIFT_CLANG_LOCATION.")

tools/SourceKit/CMakeLists.txt

@@ -8,6 +8,7 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   message(SEND_ERROR "SourceKit cannot be built standalone")
 endif()
 
+set(SOURCEKIT_SWIFT_SWAP_COMPILER FALSE)
 include(SwiftWindowsSupport)
 swift_swap_compiler_if_needed("SourceKit")
 

tools/SourceKit/cmake/modules/AddSwiftSourceKit.cmake

@@ -235,7 +235,7 @@ macro(add_sourcekit_library name)
     set(libkind)
   endif()
   add_library(${name} ${libkind} ${srcs})
-  if(NOT SWIFT_BUILT_STANDALONE AND NOT CMAKE_C_COMPILER_ID MATCHES Clang)
+  if(NOT SWIFT_BUILT_STANDALONE AND SOURCEKIT_SWIFT_SWAP_COMPILER)
     add_dependencies(${name} clang)
   endif()
   llvm_update_compile_flags(${name})
@@ -325,7 +325,7 @@ macro(add_sourcekit_executable name)
     "${SOURCEKIT_EXECUTABLE_multiple_parameter_options}" ${ARGN})
 
   add_executable(${name} ${SOURCEKITEXE_UNPARSED_ARGUMENTS})
-  if(NOT SWIFT_BUILT_STANDALONE AND NOT CMAKE_C_COMPILER_ID MATCHES Clang)
+  if(NOT SWIFT_BUILT_STANDALONE AND SOURCEKIT_SWIFT_SWAP_COMPILER)
     add_dependencies(${name} clang)
   endif()
   llvm_update_compile_flags(${name})