[llvm] [clang] [clang-tools-extra] [PowerPC] Implement llvm.set.rounding intrinsic (PR #67302)

[Qiu Chaofan via cfe-commits]

ecnelises wrote:

> The patch looks good but I am not familiar with PPC instructions enough. Could you please run the runtime tests from here: https://github.com/llvm/llvm-test-suite/tree/main/MultiSource/UnitTests/Float/rounding? You just need to build application from two files: clang rounding.c rounding-dynamic.c.

Sure. All passed on `ppc64le`, `ppc64` and `ppc32`. (of course changes to test-suite and clang are needed, I'll update then)

https://github.com/llvm/llvm-project/pull/67302