Introduce a new CodeGenInstruction::ConstraintInfo class

Introduce a new CodeGenInstruction::ConstraintInfo class
for representing constraint info semantically instead of
as a c expression that will be blatted out to the .inc
file.  Fix X86RecognizableInstr to use this instead of
parsing C code :).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95753 91177308-0d34-0410-b5e6-96231b3b80d8