[BOLT] Fix DWARFv5 for aarch64

This patch reverts patch "DWARFv5 default: Switch bolt tests to use
DWARFv4 since Bolt doesn't support v5 yet" and places the -gdwarf-4 flag
to the global cflags config file.

Reviewed By: Amir

Differential Revision: https://reviews.llvm.org/D118283