[clang] [llvm] riscv: Support -mstack-protector-guard=tls (PR #108942)

[Keith Packard via cfe-commits]

keith-packard wrote:

> LGTM. I assume you need someone to push it?

Yes please! The PowerPC one is waiting in the wings :-)

https://github.com/llvm/llvm-project/pull/108942