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

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> @jhuber6 @Meinersbur @adurang Thank you for sharing your thoughts. In that case, now that we have dependencies in liboffload, should we switch to llvm ADT in this PR or stick with the current solution until ADT runtimes are available?

They already are, the liboffload code uses LLVM's libraries everywhere, use LLVM's endianness because it's already supported between compilers.

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