[InstCombine] don't negate constant expression with fsub (PR37605)

X + (-C) would be transformed back into X - C, so infinite loop:
https://bugs.llvm.org/show_bug.cgi?id=37605


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333610 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed