Runtimes: add additional interface flags

Explicitly add the path to the Swift module to the interface include
directories. It is unclear why this is not propagating implicitly from
the module definition. For now, this ensures that the client is able to
load the standard library.

Author: compnerd

Runtimes/Core/core/CMakeLists.txt

@@ -292,14 +292,17 @@ target_compile_options(swiftCore PRIVATE
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -group-info-path -Xfrontend ${CMAKE_CURRENT_SOURCE_DIR}/GroupInfo.json>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -disable-objc-attr-requires-foundation-module>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -require-explicit-availability=ignore>")
-
 if(NOT "${CMAKE_BUILD_TYPE}" STREQUAL "MinSizeRel")
   # Using these in MinSizeRel would result in a 15% increase in the binary size
   target_compile_options(swiftCore PRIVATE
     "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xllvm -sil-inline-generics>"
     "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xllvm -sil-partial-specialization>")
 endif()
 
+# FIXME: Why is this not implicitly in the interface flags?
+target_include_directories(swiftCore INTERFACE
+  "$<$<COMPILE_LANGUAGE:Swift>:$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>$<INSTALL_INTERFACE:$<INSTALL_PREFIX>/${SwiftCore_INSTALL_SWIFTMODULEDIR}>>")
+
 target_link_libraries(swiftCore
   PRIVATE
     swiftRuntime