cfg.mk: Introduce rule for setlocale()

In the past we had some issues where setlocale() was called without
corresponding include of locale.h. While on some systems this may
work, on others the compilation failed. We should have a syntax-check
rule for that to prevent this from happening again.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

cfg.mk

@@ -929,6 +929,15 @@ sc_prohibit_mixed_case_abbreviations:
 	halt='Use PCI, USB, SCSI, not Pci, Usb, Scsi'	\
 	  $(_sc_search_regexp)
 
+# 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;
+
 # We don't use this feature of maint.mk.
 prev_version_file = /dev/null