re PR bootstrap/90543 (Build failure on MINGW for gcc-9.1.0)

re PR bootstrap/90543 (Build failure on MINGW for gcc-9.1.0)

	PR bootstrap/90543
	* optc-save-gen.awk: In cl_optimization_print, use correct condition
	for var_opt_string printing.  In cl_optimization_print_diff, print
	(null) instead of invoking undefined behavior if one of the
	var_opt_string pointers is NULL and use && instead of first || in the
	guarding condition.  For var_target_other options, handle const char *
	target variables similarly to const char * optimize node variables.

From-SVN: r271736