[Bug middle-end/127786] Combining two evaluated FP comparisons drops FE_INVALID under -ftrapping-math

[igor at tachyum dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127786

--- Comment #2 from Igor Shevlyakov <igor at tachyum dot com> ---
my patch is somewhat backported from 15.2 which didn't have ifcombine fix. I'll
try to re-work it for better fit to the trunk state