libgloss: Fix default.mh build error

Pulled from newlib upstream:

| 2014-01-10  Jeff Johnston  <jjohnstn@redhat.com>
|
|         * arm/configure.in: Revert previous fix and change host_makefile_frag
|         to calculate the absolute location of srcdir/../config/default.mh.
|         * arm/configure: Regenerated.