[clang] [clang] Lower modf builtin using `llvm.modf` intrinsic (PR #126750)

[Benjamin Maxwell via cfe-commits]

MacDue wrote:

> From this patch? https://lab.llvm.org/buildbot/#/builders/72/builds/8380
> 
> FYI @fmayer

Looks like it, I had missed it in the log but the actual error is:
> ExpandFloatResult #0: t57: ppcf128,ppcf128 = fmodf ConstantFP:ppcf128<APFloat(4611911198408756429)>, llvm-project/compiler-rt/lib/msan/tests/msan_test.cpp:1906:3
> fatal error: error in backend: Do not know how to expand the result of this operator!

I'll see if I can prepare a fix.

https://github.com/llvm/llvm-project/pull/126750