syntax-check: fix violations and re-enable sc_file_system.

syntax-check: fix violations and re-enable sc_file_system.

* cfg.mk (local-checks-to-fix): Remove sc_file_system from list
of disabled checks.
(VC_LIST_ALWAYS_EXCLUDE_REGEX): Match mail directory correctly
to avoid running its contents through syntax-check.
* build-aux/ltmain.m4sh (func_mode_link): Use correct spelling
for "file system".
* libltdl/ltdl.c (try_dlopen): Ditto.
* tests/dlloader-api.at: Ditto.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>