A lot of syntax check rules have to be rewritten, but the
result is easier to maintain.  I tested each syntax rule
by intentionally introducing a temporary violation of the rule.
Additionally, some false positives for unmarked_diagnostics
crept in, and an improved copyright_format test caught some bugs.

* .gnulib: Update to latest.
* cfg.mk (sc_prohibit_test_minus_ao): Delete, it was moved into
gnulib's maint.mk.
(sc_avoid_write, sc_prohibit_strcmp_and_strncmp)
(sc_prohibit_asprintf, sc_prohibit_strncpy, sc_prohibit_readlink)
(sc_prohibit_gethostname, sc_prohibit_gettext_noop)
(sc_prohibit_VIR_ERR_NO_MEMORY, sc_prohibit_nonreentrant)
(sc_prohibit_ctype_h, sc_TAB_in_indentation)
(sc_avoid_ctype_macros)
(sc_prohibit_virBufferAdd_with_string_literal)
(sc_prohibit_gethostby, sc_copyright_format): Rewrite in terms of
new maint.mk macros.
(sc_libvirt_unmarked_diagnostics): Fix whitespace.
* .x-sc_unmarked_diagnostics: New file.
* tests/object-locking.ml: Fix copyright.
* tools/virt-pki-validate.in: Likewise.
* tools/virt-xml-validate.in: Likewise.