[clang] [clang] Strict aliasing warning ala GCC [PR50066] (PR #74155)

[Nathan Sidwell via cfe-commits]

urnathan wrote:

> FWIW the GCC doc is https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wstrict-aliasing_003dn It says for Level 3 "If optimization is enabled, it also runs in the back end, where it deals with multiple statement cases using flow-sensitive points-to information."
> 
> Do you know how it works? Any example?

I do not now how it works -- didn't go poking there.  Neither do I have examples.

https://github.com/llvm/llvm-project/pull/74155