gdb-7.7 test failures

[Mark H Weaver]

I've done some experimenting on my systems, and the pattern seems to be
this:

* On multiprocessor machines with #:parallel-tests? enabled, gdb-7.7
  successfully builds.

* On single-processor machines, or with #:parallel-tests? disabled, the
  build always fails because "make check" fails.

Therefore, building gdb-7.7 always fails on my YeeLoong, no matter the
setting of #:parallel-tests?, presumably because that machine has only a
single processor.

Building gdb-7.7 on the Loongson 3A machine or my dual-core x86_64
machine works, but if I add "#:parallel-tests? #f" then the build fails
on both of these machines.

I think we should disable tests in gdb before the 0.6 release.
What do you think?

    Mark