[CMake] Use 'SWIFT_HOST_TRIPLE' to set '-target'

Author: rintaro

cmake/modules/AddSwiftHostLibrary.cmake

@@ -83,6 +83,12 @@ function(add_swift_syntax_library name)
         $<$<COMPILE_LANGUAGE:Swift>:-wmo>)
   endif()
 
+  if(SWIFT_HOST_TRIPLE)
+    target_compile_options("${name}" PRIVATE
+      $<$<COMPILE_LANGUAGE:Swift>:-target;${SWIFT_HOST_TRIPLE};>
+    )
+  endif()
+
   if(LLVM_USE_LINKER)
     target_link_options(${name} PRIVATE
       "-use-ld=${LLVM_USE_LINKER}"