Add mcheck tests to malloc

Like malloc-check, add generic rules to run all tests in malloc by
linking with libmcheck.a so as to provide coverage for mcheck().
Currently the following 12 tests fail:

FAIL: malloc/tst-malloc-backtrace-mcheck
FAIL: malloc/tst-malloc-fork-deadlock-mcheck
FAIL: malloc/tst-malloc-stats-cancellation-mcheck
FAIL: malloc/tst-malloc-tcache-leak-mcheck
FAIL: malloc/tst-malloc-thread-exit-mcheck
FAIL: malloc/tst-malloc-thread-fail-mcheck
FAIL: malloc/tst-malloc-usable-static-mcheck
FAIL: malloc/tst-malloc-usable-static-tunables-mcheck
FAIL: malloc/tst-malloc-usable-tunables-mcheck
FAIL: malloc/tst-malloc_info-mcheck
FAIL: malloc/tst-memalign-mcheck
FAIL: malloc/tst-posix_memalign-mcheck

and they have been added to tests-exclude-mcheck for now to keep
status quo.  At least the last two can be attributed to bugs in
mcheck() but I haven't fixed them here since they should be fixed by
removing malloc hooks.  Others need to be triaged to check if they're
due to mcheck bugs or due to actual bugs.

Reviewed-by: DJ Delorie <dj@redhat.com>