DWARF compression appears to break GDB on mips for reasons unknown. Skip
the GDB tests there.

Fixes #25939.

Change-Id: Id76860d3a2ff8055999ac12ea891c37565bb6685
Reviewed-on: https://go-review.googlesource.com/119539


Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>