IRBuilder: Move fast math flags to IRBuilderBase.

They don't depend on the templated stuff.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191672 91177308-0d34-0410-b5e6-96231b3b80d8
IRBuilder: Add RAII objects to reset insertion points or fast math flags.

Inspired by the object from the SLPVectorizer. This found a minor bug in the
debug loc restoration in the vectorizer where the location of a following
instruction was attached instead of the location from the original instruction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191673 91177308-0d34-0410-b5e6-96231b3b80d8
InstCombine: Replace manual fast math flag copying with the new IRBuilder RAII helper.

Defines away the issue where cast<Instruction> would fail because constant
folding happened. Also slightly cleaner.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191674 91177308-0d34-0410-b5e6-96231b3b80d8