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

[Kiran Chandramohan via cfe-commits]

https://github.com/kiranchandramohan commented:

> After https://github.com/llvm/llvm-project/pull/120165 clang started complaining about unknown option -f[no-]realloc-lhs.

Was this on an existing test?

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