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

[Joseph Huber via llvm-commits]

jhuber6 wrote:

Yeah, liboffload is already strongly a C++ library (something I'd change if I reworte it). This is not lib `libomp`.

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