[clang] [clang][PowerPC] Enable IEEE-128 long double on FreeBSD/powerpc64le (PR #201298)

[Piotr Kubaj via cfe-commits]

pkubaj wrote:

> What's the story with the runtimes? Since I left feedback here I came across the following comment of yours in the FreeBSD review (https://reviews.freebsd.org/D57388#1314874):
> 
> > compiler-rt part can't be upstreamed, because this is a hack -
> > compiler-rt does not support kf type ldbl functions that powerpc64le
> > needs. Upstream usually just uses libgcc (from GCC) for that.
> 
> We can't just go changing ABI if it's going to break runtimes, and any requisite support needs to go upstream first.

The story is that compiler_rt lacks proper support. It's not FreeBSD-specific, the issue is also present on Linux. On Linux it's also done the hacky way - libgcc does sed-renaming TF symbols to KF and clang links with -lgcc. The proper way would be to write independent code in compiler_rt, but that is another project on its own (probably much bigger than this). As much as I'd like it to happen, I understand that this may not make much sense since TF functions work the same as KF, so simple renaming works fine and doesn't introduce new bugs.

https://github.com/llvm/llvm-project/pull/201298