[clang] [Clang][CodeGen] Add workaround for old glibc `__PTR_ALIGN` macro (PR #137851)

[David Truby via cfe-commits]

DavidTruby wrote:

This fixes an issue I was seeing caused by #130742 that caused GNU m4 and make builds to segfault, which I assume was caused by #137833. I don't understand the code here well enough to give an actual review, but it'd be great to see this merged as m4/make builds generating bad binaries is causing a lot of other issues.
Thanks for the fix 🙂 

https://github.com/llvm/llvm-project/pull/137851