[gdb/contrib] Require minimal dwz version in cc-with-tweaks.sh

[gdb/contrib] Require minimal dwz version in cc-with-tweaks.sh

I usually run target boards cc-with-dwz and cc-with-dwz-m using a dwz build
from current trunk, but the pathname to the build dir changed and I forgot to
update my test scripts, so the test scripts reverted to using system dwz,
version 0.12.

Consequently, I ran into:
...
(gdb) p ZERO^M
No symbol "ZERO" in current context.^M
(gdb) FAIL: gdb.base/enumval.exp: p ZERO
...
which is due to PR dwz/24468, which was fixed in version 0.13.

Fix this by minimally requiring dwz version 0.13 in cc-with-tweaks.sh, such
that this situation is detected and we get instead:
...
gdb compile failed, cc-with-tweaks.sh: dwz version 0.12 detected, version \
  0.13 or higher required
...

Tested on x86_64-linux, verified with shellcheck.

Approved-By: Tom Tromey <tom@tromey.com>