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

[Slava Zakharin via cfe-commits]

vzakhari wrote:

> > After #120165 clang started complaining about unknown option -f[no-]realloc-lhs.
> 
> Was this on an existing test?

I noticed it when trying to compile a Fortran/C mix test where flang/clang were used as compilers and I passed `-fno-realloc-lhs` in flags that were used for both. Maybe it is not the right way to do it, but clang just ignored the option before my previous change.

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