maintcheck: reduce code duplication, increase coverage * syntax-checks.mk: Move ... (sc_tests_plain_aclocal, sc_tests_plain_autoconf, sc_tests_plain_perl, sc_tests_plain_autoupdate, sc_tests_plain_automake, sc_tests_plain_make, sc_tests_plain_autoheader, sc_tests_plain_autoreconf, sc_tests_plain_autom4te): ... all these targets ... (sc_tests_plain_egrep_fgrep): ... and part of this target ... (sc_tests_plain_check_rules): ... into this variable, and reimplement their recipes ... ($(sc_tests_plain_check_rules)): ... with this static pattern rule. Enhance the coverage they offer a little since we are at it. (sc_m4_am_plain_egrep_fgrep): New rule, the part of the old 'sc_tests_plain_egrep_fgrep' rule that checked for use of 'fgrep' and 'egrep' in *.am and *.m4 fragments (rather than in test scripts). (syntax_check_rules): Update. * t/dist-formats.tap: Fix bad use of "make" instead of "$MAKE" revealed by the extra coverage. * t/cond5.sh, t/auxdir-autodetect.sh: Cosmetic changes to avoid spuriously triggering the maintainer checks due to the enhanced coverage. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>