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:
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.