gcc-runtime: Add do_check task for executing gcc test suites

gcc-runtime: Add do_check task for executing gcc test suites

Add a do_check task to implement execution of the gcc component test
suites. The component test suites require execution of compiled programs
on the target.

The implementation provided allows for execution testing against a host
via SSH or within the local build environment using qemu linux-user
execution. The selection of execution is done via the
TOOLCHAIN_TEST_TARGET variable, and configuration of the remote host is
done with the TOOLCHAIN_TEST_HOST, TOOLCHAIN_TEST_HOST_USER and
TOOLCHAIN_TEST_HOST_PORT variables.

By default the do_check task will execute all check targets, this can be
changed by setting MAKE_CHECK_TARGETS to the desired test suite target
(e.g. check-gcc or check-target-libatomic).

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>