[flang] [libc] [compiler-rt] [clang] [clang-tools-extra] [llvm] [libcxx] [lld] [lldb] [NVPTX] Add support for -march=native in standalone NVPTX (PR #79373)

[Justin Lebar via cfe-commits]

jlebar wrote:

Got it, okay, thanks.

Since this change only applies to `--target=nvptx64-nvidia-cuda`, fine by me.  Thanks for putting up with our scrutiny.  :)

https://github.com/llvm/llvm-project/pull/79373