[FPEnv] Expand constrained FP POWI

Modify ExpandStrictFPOp(...) to handle nodes that have scalar
operands. 

Also, add a Strict FMA test and do some other light cleanup in the
Strict FP code.

Differential Revision: https://reviews.llvm.org/D48149



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334863 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed