[CMake] Set CMAKE_{C|CXX}_COMPILER_TARGET for swift-syntax

swift-syntax now have '.c' sources. We need to set this for
cross-compiling.

Author: rintaro

lib/CompilerSwiftSyntax/CMakeLists.txt

@@ -8,6 +8,10 @@ endif()
 
 # Build swift-syntax libraries with FetchContent.
 function(includeSwiftSyntax)
+  set(CMAKE_SYSTEM_PROCESSOR ${SWIFT_HOST_VARIANT_ARCH})
+  set(CMAKE_OSX_ARCHITECTURES ${SWIFT_HOST_VARIANT_ARCH})
+  set(CMAKE_C_COMPILER_TARGET ${SWIFT_HOST_TRIPLE})
+  set(CMAKE_CXX_COMPILER_TARGET ${SWIFT_HOST_TRIPLE})
   set(CMAKE_Swift_COMPILER_TARGET ${SWIFT_HOST_TRIPLE})
   set(BUILD_SHARED_LIBS ON)
   set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${SWIFT_HOST_LIBRARIES_DEST_DIR}/compiler")

lib/SwiftSyntax/CMakeLists.txt

@@ -7,6 +7,10 @@ if(NOT EXISTS "${SWIFT_PATH_TO_SWIFT_SYNTAX_SOURCE}")
 endif()
 
 # Build swift-syntax libraries with FetchContent.
+set(CMAKE_SYSTEM_PROCESSOR ${SWIFT_HOST_VARIANT_ARCH})
+set(CMAKE_OSX_ARCHITECTURES ${SWIFT_HOST_VARIANT_ARCH})
+set(CMAKE_C_COMPILER_TARGET ${SWIFT_HOST_TRIPLE})
+set(CMAKE_CXX_COMPILER_TARGET ${SWIFT_HOST_TRIPLE})
 set(CMAKE_Swift_COMPILER_TARGET ${SWIFT_HOST_TRIPLE})
 set(BUILD_SHARED_LIBS ON)
 # All libraries in 'swift-syntax' goes to 'lib/swift/host'.