[CMake] Don't export module map for Windows after the first installed SDK arch, as unneeded after swiftlang/swift#79621

Author: finagolfin

Sources/_FoundationCShims/CMakeLists.txt

@@ -19,8 +19,10 @@ add_library(_FoundationCShims STATIC
 
 target_include_directories(_FoundationCShims PUBLIC include)
 
-target_compile_options(_FoundationCShims INTERFACE
-  "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xcc -fmodule-map-file=${CMAKE_CURRENT_SOURCE_DIR}/include/module.modulemap>")
+if(CMAKE_SYSTEM_NAME STREQUAL "Windows" AND NOT BUILT_FIRST_SDK)
+  target_compile_options(_FoundationCShims INTERFACE
+    "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xcc -fmodule-map-file=${CMAKE_CURRENT_SOURCE_DIR}/include/module.modulemap>")
+endif()
 
 set_property(GLOBAL APPEND PROPERTY SWIFT_FOUNDATION_EXPORTS _FoundationCShims)