Runtimes: avoid ODR violations in _Concurrency

When building the standard libraries with the LLVM ADT types, we use the
local definition which have been modified to avoid ODR violations.
However, due to the intermingling of the compiler and runtime
implementations, we cannot isolate the headers properly to ensure that
the right definition is used. We need to ensure that we pass along
`SWIFT_RUNTIME` when processing headers to avoid references to the
unsafe references to the LLVM Support library.

Author: compnerd

Runtimes/Core/Concurrency/CMakeLists.txt

@@ -102,6 +102,7 @@ add_library(swift_Concurrency
 
 include(${SwiftCore_CONCURRENCY_GLOBAL_EXECUTOR}.cmake)
 target_compile_definitions(swift_Concurrency PRIVATE
+  $<$<COMPILE_LANGUAGE:C,CXX>:-DSWIFT_RUNTIME>
   $<$<COMPILE_LANGUAGE:C,CXX>:-DSWIFT_TARGET_LIBRARY_NAME=swift_Concurrency>
   # NOTE: VS2017 <15.8 would round clamp alignment to alignof(max_align_t) which
   # was non-conformant. Indicate that we wish to use extended alignment.