[clang] [flang] Ignore -f[no-]realloc-lhs. (PR #120320)

[Slava Zakharin via cfe-commits]

vzakhari wrote:

Okay, I do not see an easy way to allow this option for `clang` without printing it in the `--help` output, so I guess I will let it behave same way as the other Flang-only options.

https://github.com/llvm/llvm-project/pull/120320