ifcvt: Fix rtl checking due to reversed_comparison_code returning UNKNOWN [PR124062]

ifcvt: Fix rtl checking due to reversed_comparison_code returning UNKNOWN [PR124062]

This was an oversight on my part (after r16-6435-g594f2cbf30f0a3)
where I forgot that sometimes reversed_comparison_code will return
UNKNOWN when the floating point comparison can't be reversed.
This seems only to show up with RTL checking only; at least as far
as I can tell because it is rejected later on but I could be wrong.

Bootstrapped and tested on x86_64-linux-gnu.

	PR rtl-optimization/124062

gcc/ChangeLog:

	* ifcvt.cc (noce_try_cond_arith): Check the conditional code
	for UNKNOWN.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr124062-1.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>