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

[Joseph Huber via llvm-commits]

jhuber6 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.

We do get this problem in practice, where people compile LLVM w/ libstdc++ and the runtimes with libc++ for example. Creates a bit of a mess because we are the only runtime that depends on LLVM libraries for shipped runtimes, but it's existing behavior.

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