Check for NoNaNsFPMath function attribute in isKnownNeverSNaN.
Function attributes are in held in 'TargetMachine.Options'.
Among other things, this allows selection of some patterns imported
in D87351 since G_FCANONICALIZE is not generated when isKnownNeverSNaN
returns true in lowerFMinNumMaxNum.
However we notice some incorrect results since function attributes are
not correctly written in TargetMachine.Options when next function is
processed. Look at @v_test_no_global_nnans_med3_f32_pat0_srcmod0, it has
"no-nans-fp-math"="false" but TargetMachine.Options still has it set to
true since first function in test file had this attribute set to true.
This will be fixed by in D87511.