build: improve debug builds on Windows

Ensure that we build all the target libraries with the correct build
configuration.  This is needed on Windows where the different MSVC
runtime libraries are ABI incompatible.

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -1914,6 +1914,20 @@ function(add_swift_target_library name)
         GYB_SOURCES ${SWIFTLIB_GYB_SOURCES}
       )
 
+      if(sdk STREQUAL WINDOWS)
+        if(SWIFT_COMPILER_IS_MSVC_LIKE)
+          if (SWIFT_STDLIB_MSVC_RUNTIME_LIBRARY MATCHES MultiThreadedDebugDLL)
+            target_compile_options(${VARIANT_NAME} PRIVATE /MDd /D_DLL /D_DEBUG)
+          elseif (SWIFT_STDLIB_MSVC_RUNTIME_LIBRARY MATCHES MultiThreadedDebug)
+            target_compile_options(${VARIANT_NAME} PRIVATE /MTd /U_DLL /D_DEBUG)
+          elseif (SWIFT_STDLIB_MSVC_RUNTIME_LIBRARY MATCHES MultiThreadedDLL)
+            target_compile_options(${VARIANT_NAME} PRIVATE /MD /D_DLL /U_DEBUG)
+          elseif (SWIFT_STDLIB_MSVC_RUNTIME_LIBRARY MATCHES MultiThreaded)
+            target_compile_options(${VARIANT_NAME} PRIVATE /MT /U_DLL /U_DEBUG)
+          endif()
+        endif()
+      endif()
+
       if(NOT SWIFTLIB_OBJECT_LIBRARY)
         # Add dependencies on the (not-yet-created) custom lipo target.
         foreach(DEP ${SWIFTLIB_LINK_LIBRARIES})