[cxx-interop][SwiftCompilerSources] Enable libstdc++ on platforms that use it

Since libstdc++ doesn't come with a Clang modulemap, Swift provides its own modulemap for libstdc++. This change makes the modulemap available while building SwiftCompilerSources.

Author: egorzhdan

SwiftCompilerSources/CMakeLists.txt

@@ -212,6 +212,10 @@ else()
         list(APPEND b0_deps swiftDarwin-bootstrapping0)
         list(APPEND b1_deps swiftDarwin-bootstrapping1)
       endif()
+      if(${SWIFT_HOST_VARIANT_SDK} IN_LIST SWIFT_LIBSTDCXX_PLATFORMS)
+        list(APPEND b0_deps copy-libstdcxx-modulemap-bootstrapping0 copy-libstdcxx-header-bootstrapping0)
+        list(APPEND b1_deps copy-libstdcxx-modulemap-bootstrapping1 copy-libstdcxx-header-bootstrapping1)
+      endif()
     endif()
     if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS)
       set(platform ${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR})

cmake/modules/AddSwift.cmake

@@ -3,6 +3,7 @@ include(SwiftList)
 include(SwiftXcodeSupport)
 include(SwiftWindowsSupport)
 include(SwiftAndroidSupport)
+include(SwiftCXXUtils)
 
 function(_swift_gyb_target_sources target scope)
   file(GLOB GYB_UNICODE_DATA ${SWIFT_SOURCE_DIR}/utils/UnicodeData/*)

cmake/modules/SwiftCXXUtils.cmake

@@ -0,0 +1,7 @@
+# Platforms that use libstdc++ as the system-wide default C++ standard library.
+set(SWIFT_LIBSTDCXX_PLATFORMS
+    "LINUX"
+    "FREEBSD"
+    "OPENBSD"
+    "CYGWIN"
+    "HAIKU")

stdlib/public/Cxx/CMakeLists.txt

@@ -1,10 +1,6 @@
 set(libstdcxx_modulemap_target_list)
 foreach(sdk ${SWIFT_SDKS})
-  if(NOT "${sdk}" STREQUAL "LINUX" AND
-      NOT "${sdk}" STREQUAL "FREEBSD" AND
-      NOT "${sdk}" STREQUAL "OPENBSD" AND
-      NOT "${sdk}" STREQUAL "CYGWIN" AND
-      NOT "${sdk}" STREQUAL "HAIKU")
+  if(NOT ${sdk} IN_LIST SWIFT_LIBSTDCXX_PLATFORMS)
     continue()
   endif()
 
@@ -89,6 +85,38 @@ foreach(sdk ${SWIFT_SDKS})
           DESTINATION "lib/swift_static/${arch_subdir}"
           COMPONENT sdk-overlay)
     endif()
+
+    if(${BOOTSTRAPPING_MODE} MATCHES "BOOTSTRAPPING.*")
+      foreach(bootstrapping "0" "1")
+        get_bootstrapping_path(bootstrapping_dir ${module_dir} ${bootstrapping})
+        set(libstdcxx_modulemap_out_bootstrapping "${bootstrapping_dir}/libstdcxx.modulemap")
+        set(libstdcxx_header_out_bootstrapping "${bootstrapping_dir}/libstdcxx.h")
+
+        add_custom_command_target(unused_var
+            COMMAND
+            "${CMAKE_COMMAND}" "-E" "make_directory" "${bootstrapping_dir}"
+            COMMAND
+            "${CMAKE_COMMAND}" "-E" "copy"
+            "${CMAKE_CURRENT_SOURCE_DIR}/${libstdcxx_modulemap}" "${libstdcxx_modulemap_out_bootstrapping}"
+
+            CUSTOM_TARGET_NAME "copy-libstdcxx-modulemap-bootstrapping${bootstrapping}"
+            OUTPUT "${libstdcxx_modulemap_out_bootstrapping}"
+            DEPENDS ${libstdcxx_modulemap}
+            COMMENT "Copying libstdcxx modulemap to resources for bootstrapping${bootstrapping}")
+
+        add_custom_command_target(unused_var
+            COMMAND
+            "${CMAKE_COMMAND}" "-E" "make_directory" "${bootstrapping_dir}"
+            COMMAND
+            "${CMAKE_COMMAND}" "-E" "copy"
+            "${CMAKE_CURRENT_SOURCE_DIR}/${libstdcxx_header}" "${libstdcxx_header_out_bootstrapping}"
+
+            CUSTOM_TARGET_NAME "copy-libstdcxx-header-bootstrapping${bootstrapping}"
+            OUTPUT "${libstdcxx_header_out_bootstrapping}"
+            DEPENDS ${libstdcxx_header}
+            COMMENT "Copying libstdcxx header to resources for bootstrapping${bootstrapping}")
+      endforeach()
+    endif()
   endforeach()
 endforeach()
 add_custom_target(libstdcxx-modulemap DEPENDS ${libstdcxx_modulemap_target_list})