go to great lengths to work around a GAS bug my previous patch

exposed:

GAS doesn't accept "fcomip %st(1)", it requires "fcomip %st(1), %st(0)"
even though st(0) is implicit in all other fp stack instructions.

Fortunately, there is an alias for fcomip named "fcompi" and gas does
accept the default argument for the alias (boggle!).

As such, switch the canonical form of this instruction to "pi" instead
of "ip".  This makes the code generator and disassembler generate pi,
avoiding the gas bug.

llvm-svn: 118356