[llvm] [Offload] define MSVC byte-order macros for rtl endianness checks (PR #202540)

[Alex Duran via llvm-commits]

================
@@ -33,6 +33,13 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 
+// TODO: Replace with a shared runtime endianness abstraction.
----------------
adurang wrote:

That would result in reporting the wrong Triple for win/aarch64. Not sure if that's something we need to care or not though.

https://github.com/llvm/llvm-project/pull/202540