[compiler-rt] [compiler-rt] Implement __extendxftf2 and __trunctfxf2 for x86_64 (PR #66918)

[Alexander Richardson via llvm-commits]

arichardson wrote:

Some of this can be simplified if https://github.com/llvm/llvm-project/pull/68132 lands first, but I guess the cleanups could also be done afterwards?

https://github.com/llvm/llvm-project/pull/66918