ANDROID: gki_config: use DWARFv5 rather than DWARFv4

DWARFv5 is the latest iteration of the debug info spec; it contains many
encoding tricks to optimize for space.

For example, with this patch applied (DWARFv5), for
build.config.gki.aarch64:
$ du -h out/android-mainline/dist/vmlinux
304M	out/android-mainline/dist/vmlinux

Before (DWARFv4):
du -h out/android-mainline/dist/vmlinux
339M	out/android-mainline/dist/vmlinux

Bug: 192694378
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Change-Id: I6644482d9b12eb3e0d1d3676c53ee2eee97a6573