cfg.mk: check ctype_macros only on *.[c|h] files

The functions like isalnum(), isalpha(), isdigit(), etc. are also
available in Python, however `make syntax-check` do not intend to
prohibit them.
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Signed-off-by: NRadostin Stoyanov <rstoyanov1@gmail.com>

cfg.mk

@@ -496,6 +496,7 @@ ctype_re = isalnum|isalpha|isascii|isblank|iscntrl|isdigit|isgraph|islower\
 
 sc_avoid_ctype_macros:
 	@prohibit='\b($(ctype_re)) *\(' \
+	in_vc_files='\.[ch]$$' \
 	halt='use c-ctype.h instead of ctype macros' \
 	  $(_sc_search_regexp)