[TargetLibraryInfo] Add support for fls, flsl, flsll.

This is a prerequisite for further optimisations of these functions,
which will be commited as a separate patch.

Differential Revision:	http://reviews.llvm.org/D14219


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252535 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed