SimplifyLibCalls: Replace fabs libcalls with intrinsics

Add missing fabs(fpext) optimzation that worked with the call,
and also fixes it creating a second fpext when there were multiple
uses.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292172 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed