Compile with -fshort-chars on Windows

HIP requires a short wchar on Windows, and all compilation through Comgr
on Windows now assumes the bitcode is compiled with a short wchar as
well. This is the matching change to ensure this in the device-libs.

Change-Id: Ifcf511bde8a5a198c42cb829af0c5283c11e61ed

OCL.cmake

@@ -27,6 +27,12 @@ set(CLANG_OCL_FLAGS -fcolor-diagnostics -Werror -Wno-error=atomic-alignment -x c
   -cl-std=CL2.0 -target "${AMDGPU_TARGET_TRIPLE}" -fvisibility=protected -fomit-frame-pointer
   -Xclang -finclude-default-header "${CLANG_OPTIONS_APPEND}")
 
+# For compatibility with the MSVC headers we use a 32-bit wchar. Users linking
+# against us must also use a short wchar.
+if (WIN32)
+  set(CLANG_OCL_FLAGS ${CLANG_OCL_FLAGS} -fshort-wchar)
+endif()
+
 set (BC_EXT .bc)
 set (LIB_SUFFIX ".lib${BC_EXT}")
 set (STRIP_SUFFIX ".strip${BC_EXT}")