testsuite: Disable colorization for ubsan test

testsuite: Disable colorization for ubsan test

 - Run gcc testsuite with qemu will print out ascii color code for
   ubsan related testcase, however several testcase didn't consider
   that, so disable colorization prevent such problem and simplify the
   process when adding testcase in future.

 - Verified on native X86 and RISC-V qemu full system mode and user mode.

gcc/testsuite/ChangeLog:

	* lib/ubsan-dg.exp (orig_ubsan_options_saved): New
	(orig_ubsan_options): Ditto.
	(ubsan_init): Store UBSAN_OPTIONS and set UBSAN_OPTIONS.
	(ubsan_finish): Restore UBSAN_OPTIONS.