Platform: make stdint module implicit on Windows

This makes the `stdint` module implicit which repairs the ability to
build some components.  In order to accomplish this, we need to
potentially break the fragile Swift build system.  Due to the incorrect
handling of compilers we need some workarounds to support
cross-compilation.  This removes the injected system header paths when
building on Windows to ensure that the clang resource headers are not
following the system headers which breaks the modules as the clang
resources are dependent on the system headers when running in hosted
mode.

Author: compnerd

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -491,8 +491,10 @@ function(_add_target_variant_link_flags)
       # options. This causes conflicts.
       list(APPEND result "-nostdlib")
     endif()
-    swift_windows_lib_for_arch(${LFLAGS_ARCH} ${LFLAGS_ARCH}_LIB)
-    list(APPEND library_search_directories ${${LFLAGS_ARCH}_LIB})
+    if(NOT CMAKE_HOST_SYSTEM MATCHES Windows)
+      swift_windows_lib_for_arch(${LFLAGS_ARCH} ${LFLAGS_ARCH}_LIB)
+      list(APPEND library_search_directories ${${LFLAGS_ARCH}_LIB})
+    endif()
 
     # NOTE(compnerd) workaround incorrectly extensioned import libraries from
     # the Windows SDK on case sensitive file systems.
@@ -894,10 +896,12 @@ function(add_swift_target_library_single target name)
     endif()
     list(APPEND SWIFTLIB_SINGLE_SWIFT_COMPILE_FLAGS
       -vfsoverlay;"${SWIFT_WINDOWS_VFS_OVERLAY}")
-    swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE} SWIFTLIB_INCLUDE)
-    foreach(directory ${SWIFTLIB_INCLUDE})
-      list(APPEND SWIFTLIB_SINGLE_SWIFT_COMPILE_FLAGS -Xcc;-isystem;-Xcc;${directory})
-    endforeach()
+    if(NOT CMAKE_HOST_SYSTEM MATCHES Windows)
+      swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE} SWIFTLIB_INCLUDE)
+      foreach(directory ${SWIFTLIB_INCLUDE})
+        list(APPEND SWIFTLIB_SINGLE_SWIFT_COMPILE_FLAGS -Xcc;-isystem;-Xcc;${directory})
+      endforeach()
+    endif()
     if("${SWIFTLIB_SINGLE_ARCHITECTURE}" MATCHES arm)
       list(APPEND SWIFTLIB_SINGLE_SWIFT_COMPILE_FLAGS -Xcc;-D_ARM_WINAPI_PARTITION_DESKTOP_SDK_AVAILABLE)
     endif()
@@ -1059,9 +1063,11 @@ function(add_swift_target_library_single target name)
                              SWIFT_INLINE_NAMESPACE=__runtime)
 
   if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "WINDOWS")
-    swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE} SWIFTLIB_INCLUDE)
-    target_include_directories("${target}" SYSTEM PRIVATE
-      ${SWIFTLIB_INCLUDE})
+    if(NOT CMAKE_HOST_SYSTEM MATCHES Windows)
+      swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE} SWIFTLIB_INCLUDE)
+      target_include_directories("${target}" SYSTEM PRIVATE
+        ${SWIFTLIB_INCLUDE})
+    endif()
   endif()
 
   if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "WINDOWS" AND NOT "${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
@@ -1370,10 +1376,12 @@ function(add_swift_target_library_single target name)
 
   # Set compilation and link flags.
   if(SWIFTLIB_SINGLE_SDK STREQUAL WINDOWS)
-    swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE}
-      ${SWIFTLIB_SINGLE_ARCHITECTURE}_INCLUDE)
-    target_include_directories(${target} SYSTEM PRIVATE
-      ${${SWIFTLIB_SINGLE_ARCHITECTURE}_INCLUDE})
+    if(NOT CMAKE_HOST_SYSTEM MATCHES Windows)
+      swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE}
+        ${SWIFTLIB_SINGLE_ARCHITECTURE}_INCLUDE)
+      target_include_directories(${target} SYSTEM PRIVATE
+        ${${SWIFTLIB_SINGLE_ARCHITECTURE}_INCLUDE})
+    endif()
 
     if(NOT ${CMAKE_C_COMPILER_ID} STREQUAL MSVC)
       swift_windows_get_sdk_vfs_overlay(SWIFTLIB_SINGLE_VFS_OVERLAY)
@@ -2614,10 +2622,12 @@ function(_add_swift_target_executable_single name)
   llvm_update_compile_flags("${name}")
 
   if(SWIFTEXE_SINGLE_SDK STREQUAL WINDOWS)
-    swift_windows_include_for_arch(${SWIFTEXE_SINGLE_ARCHITECTURE}
-      ${SWIFTEXE_SINGLE_ARCHITECTURE}_INCLUDE)
-    target_include_directories(${name} SYSTEM PRIVATE
-      ${${SWIFTEXE_SINGLE_ARCHITECTURE}_INCLUDE})
+    if(NOT CMAKE_HOST_SYSTEM MATCHES Windows)
+      swift_windows_include_for_arch(${SWIFTEXE_SINGLE_ARCHITECTURE}
+        ${SWIFTEXE_SINGLE_ARCHITECTURE}_INCLUDE)
+      target_include_directories(${name} SYSTEM PRIVATE
+        ${${SWIFTEXE_SINGLE_ARCHITECTURE}_INCLUDE})
+    endif()
     if(NOT ${CMAKE_C_COMPILER_ID} STREQUAL MSVC)
       # MSVC doesn't support -Xclang. We don't need to manually specify
       # the dependent libraries as `cl` does so.

stdlib/public/Platform/vcruntime.modulemap

@@ -105,7 +105,7 @@ module vcruntime [system] {
     export *
   }
 
-  explicit module stdint {
+  module stdint {
     header "stdint.h"
     export *
   }