[NFC][compiler-rt][builtins] Tidy and match comments for floating point operations

Differential Revision: https://reviews.llvm.org/D61762

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@360389 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed