maint: optimize locale.h syntax check

Reusing the maint.mk code allows for a more efficient syntax check
(fewer grep processes), and a more compact representation of what
we are really checking for in commit 1919e35.

* cfg.mk (sc_require_locale_h): Use maint.mk loop instead of
rolling our own.

Signed-off-by: Eric Blake <eblake@redhat.com>

cfg.mk

@@ -931,12 +931,10 @@ sc_prohibit_mixed_case_abbreviations:
 
 # Require #include <locale.h> in all files that call setlocale()
 sc_require_locale_h:
-	@for i in $$($(VC_LIST_EXCEPT) | grep '\.[chx]$$'); do			\
-		if ! grep -q setlocale\( $$i ; then continue; fi ;		\
-		if ! grep -q '# *include <locale.h>' $$i ; then			\
-			echo '$(ME): missing locale.h include in' $$i 1>&2; exit 1;	\
-		fi;															\
-	done;
+	@require='include.*locale\.h'					\
+	containing='setlocale *('					\
+	halt='setlocale() requires <locale.h>'				\
+	  $(_sc_search_regexp)
 
 # We don't use this feature of maint.mk.
 prev_version_file = /dev/null