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

[Michael Kruse via llvm-commits]

Meinersbur wrote:

OK then. I guess it should be changed when a runtimes ADT eventually becomes available. I guess I spent too much time with buildbots setting LLVM_ENABLE_LIBCXX and getting a mix of libcxx and libstdcxx when compiling runtimes.

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