maintcheck: fix spurious failures

maintcheck: fix spurious failures

* syntax-check.mk (sc_mkinstalldirs): Now the 'mkinstalldirs' is
listed in the top-level 'Makefile.am', not in 'lib/Makefile.am';
adjust the "whitelist" accordingly.
(sc_ensure_testsuite_has_run): The 'test-suite.log' file created by
"make check" is now placed in the top-level directory, not in the
't/' subdirectory.  Adjust by using '$(TEST_SUITE_LOG)' instead of
an hand-crafted path for the 'test-suite.log' file.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>