rs6000: Workaround for new ifcvt behavior [PR104335].

rs6000: Workaround for new ifcvt behavior [PR104335].

Since r12-6747-gaa8cfe785953a0 ifcvt passes a "cc comparison"
i.e. the representation of the result of a comparison to the
backend.  rs6000_emit_int_cmove () is not prepared to handle this.
Therefore, this patch makes it return false in such a case.

	PR target/104335

gcc/ChangeLog:

	* config/rs6000/rs6000.cc (rs6000_emit_int_cmove): Return false
	if the expected comparison's first operand is of mode MODE_CC.