[PR103437] Make backup code for overflow conditional

[PR103437] Make backup code for overflow conditional

Switch off long long variant overflow code by preprocessor if the
build compiler has __builtin_smul_overflow.

gcc/ChangeLog:
	PR rtl-optimization/103437
	* ira-color.c (setup_allocno_priorities): Switch off backup code
	for overflow if compiler has __builtin_smul_overflow.  Use <
	for comparison with -INT_MAX.