In some cases of overriding or resetting locations, we might retain
discriminator info from earlier locations, when we should take
discriminator information from the overriding location or reset it.
for gcc/ChangeLog
* final.c (compute_discriminator): Declare. Renamed from...
(maybe_set_discriminator): ... this. Set and return a local.
(override_discriminator): New.
(final_scan_insn_1): Set it.
(notice_source_line): Adjust. Always set discriminator.