Runtimes: inject Windows SDK clang modules

When building the standard library, the SDK is not fully staged and so
the compiler would not be able to inject the VFS overlay for the
modularisation of the Windows SDK. Manually construct the mappings and
apply them.

Author: compnerd

Runtimes/Overlay/Windows/CRT/CMakeLists.txt

@@ -14,6 +14,7 @@ target_compile_definitions(swiftCRT PRIVATE
 target_compile_options(swiftCRT PRIVATE
   "SHELL:-Xcc -D_USE_MATH_DEFINES")
 target_link_libraries(swiftCRT PRIVATE
+  ClangModules
   swiftCore)
 
 install(TARGETS swiftCRT

Runtimes/Overlay/Windows/WinSDK/CMakeLists.txt

@@ -6,6 +6,7 @@ set_target_properties(swiftWinSDK PROPERTIES
 target_compile_definitions(swiftCRT PRIVATE
   $<$<BOOL:${SwiftOverlay_ENABLE_REFLECTION}>:SWIFT_ENABLE_REFLECTION>)
 target_link_libraries(swiftWinSDK PRIVATE
+  ClangModules
   swiftCore)
 
 install(TARGETS swiftWinSDK

Runtimes/Overlay/Windows/clang/CMakeLists.txt

@@ -1,4 +1,46 @@
 
+file(TO_CMAKE_PATH "$ENV{WindowsSdkDir}" WindowsSdkDir)
+file(TO_CMAKE_PATH "$ENV{WindowsSDKVersion}" WindowsSDKVersion)
+file(TO_CMAKE_PATH "$ENV{UniversalCRTSdkDir}" UniversalCRTSdkDir)
+file(TO_CMAKE_PATH "$ENV{UCRTVersion}" UCRTVersion)
+file(TO_CMAKE_PATH "$ENV{VCToolsInstallDir}" VCToolsInstallDir)
+
+file(CONFIGURE
+  OUTPUT windows-sdk-overlay.yaml
+  CONTENT [[
+---
+version: 0
+case-sensitive: false
+use-external-names: false
+roots:
+  - name: "@WindowsSdkDir@/Include/@WindowsSDKVersion@/um"
+    type: directory
+    contents:
+      - name: module.modulemap
+        type: file
+        external-contents: "@CMAKE_CURRENT_SOURCE_DIR@/winsdk.modulemap"
+  - name: "@UniversalCRTSdkDir@/Include/@UCRTVersion@/ucrt"
+    type: directory
+    contents:
+      - name: module.modulemap
+        type: file
+        external-contents: "@CMAKE_CURRENT_SOURCE_DIR@/ucrt.modulemap"
+  - name: "@VCToolsInstallDir@include"
+    type: directory
+    contents:
+      - name: module.modulemap
+        type: file
+        external-contents: "@CMAKE_CURRENT_SOURCE_DIR@/vcruntime.modulemap"
+      - name: vcruntime.apinotes
+        type: file
+        external-contents: "@CMAKE_CURRENT_SOURCE_DIR@/vcruntime.apinotes"
+]]
+ESCAPE_QUOTES @ONLY NEWLINE_STYLE LF)
+
+add_library(ClangModules INTERFACE)
+target_compile_options(ClangModules INTERFACE
+  "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-vfsoverlay ${CMAKE_CURRENT_BINARY_DIR}/windows-sdk-overlay.yaml>")
+
 install(FILES
   ucrt.modulemap
   vcruntime.apinotes

Runtimes/Overlay/clang/CMakeLists.txt

@@ -9,6 +9,7 @@ set_target_properties(swift_Builtin_float PROPERTIES
 target_compile_options(swift_Builtin_float PRIVATE
   "$<$<PLATFORM_ID:Darwin>:SHELL:-Xfrontend -module-abi-name -Xfrontend Darwin>")
 target_link_libraries(swift_Builtin_float PRIVATE
+  $<$<PLATFORM_ID:Windows>:ClangModules>
   swiftCore)
 
 install(TARGETS swift_Builtin_float