Runtimes: add interface include directories for _Concurrency

Ensure that the _Concurrency module is properly made available to the
users who link against it.

Author: compnerd

Runtimes/Core/Concurrency/CMakeLists.txt

@@ -122,6 +122,9 @@ target_include_directories(swift_Concurrency PRIVATE
   # FIXME: grant access to `runtime/CMakeConfig.h` which should be available
   # through the swiftRuntime target.
   "${PROJECT_BINARY_DIR}/include")
+# FIXME: Why is this not implicitly in the interface flags?
+target_include_directories(swift_Concurrency INTERFACE
+  "$<$<COMPILE_LANGUAGE:Swift>:$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>$<INSTALL_INTERFACE:$<INSTALL_PREFIX>/${SwiftCore_INSTALL_SWIFTMODULEDIR}>>")
 target_link_libraries(swift_Concurrency PRIVATE
   swiftShims
   swiftConcurrencyInternalShims