[clang] [clang][cmake] Don't pass -fno-strict-aliasing for GCC (PR #144222)

[Sam James via cfe-commits]

thesamesam wrote:

Huh, I thought I'd written a reply to nikic but I don't see it here? Anyway, rewriting it..

> To confirm, you do not get any -Wstrict-aliasing warnings with modern GCC after this change?

Yes. Sorry, it's obvious in hindsight I should've stated this explicitly.

https://github.com/llvm/llvm-project/pull/144222