[clang] [llvm] [PowerPC][ISelLowering] Support -mstack-protector-guard=tls (PR #110928)

[Stewart Smith via cfe-commits]

stewartsmith wrote:

It's been a few years (and I've spent more time in 16bit x86 than powerpc for a while), but I'm pretty sure this looks good.

While the POWER ISA may be lacking vowels, the lack of `r` denoting registers in the test llvm test suite is (at least for me) doing it on hard mode :)

https://github.com/llvm/llvm-project/pull/110928