[flang] [llvm] [flang-rt] Implement basic support for I/O from OpenMP GPU Offloading (PR #181039)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

Changed it to still build without `libc/` in tree. Let me know if that's okay, or if we should just require it anyway.

https://github.com/llvm/llvm-project/pull/181039