gdb/testsuite: add a new check-all-boards target

The make-check-all.sh script (gdb/testsuite/make-check-all.sh) is
great, it makes it super easy to run some test(s) using all the
available board files.

This commit aims to make this script even easier to access by adding a
check-all-boards target to the GDB Makefile.  This new target checks
for (and requires) a number of environment variables, so the target
should be used like this:

  make check-all-boards GDB_TARGET_USERNAME=remote-target \
                        GDB_HOST_USERNAME=remote-host \
			TESTS="gdb.base/break.exp"

Where GDB_TARGET_USERNAME and GDB_HOST_USERNAME are the user names
that should be passed to the make-check-all.sh --target-user and
--host-user command line options respectively.

My personal intention is to set these variables in my environment, so
all I'll need to do is:

  make check-all-boards TESTS="gdb.base/break.exp"

The make rule always passes --keep-results to the make-check-all.sh
script, as I find that the most useful.  It's super frustrating to run
the tests and realise you forgot that option and the results have been
discarded.
3 files changed