Change the fp to integer code to not perform 2-byte stores followed by

1 byte loads and other operations.  This is bad for store-forwarding on
common CPUs.  We now do this:

fnstcw WORD PTR [%ESP]
mov %AX, WORD PTR [%ESP]

instead of:

fnstcw WORD PTR [%ESP]
mov %AL, BYTE PTR [%ESP + 1]

llvm-svn: 22559