[binutils-gdb/gdb-7.9-branch] Fix the triplet regexp to recognize triplets, not only quadruplets

[sergiodj+buildbot@redhat.com]

*** TEST RESULTS FOR COMMIT 2e9f68f0cf32bad824100dfb5d05c4235cf59ff3 ***

Author: Matthias Klose <doko@ubuntu.com>
Branch: gdb-7.9-branch
Commit: 2e9f68f0cf32bad824100dfb5d05c4235cf59ff3

Fix the triplet regexp to recognize triplets, not only quadruplets
This allows triplets where the vendor is not set.

gdb/ChangeLog:
2015-03-31  Matthias Klose  <doko@ubuntu.com>

	* compile/compile.c (compile_to_object): Allow triplets with or
	without vendor set.