Factor out the predicate check code from DAGISelEmitter.cpp

Factor out the predicate check code from DAGISelEmitter.cpp
and use it in FastISelEmitter.cpp, and make FastISel
subtarget aware. Among other things, this lets it work
properly on x86 targets that don't have SSE, where it
successfully selects x87 instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55156 91177308-0d34-0410-b5e6-96231b3b80d8