Implement PR6845. We allow matching constraints to have different

Implement PR6845.  We allow matching constraints to have different
input and output types when the smaller value isn't mentioned in the
asm string.  Extend this support from integers to also allowing
fp values to be mismatched (if not mentioned in the asm string).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102188 91177308-0d34-0410-b5e6-96231b3b80d8