grobian@gentoo.org: include string.h so memset is declared

--- a/src/libspf2/spf_utils.c
+++ b/src/libspf2/spf_utils.c
@@ -19,6 +19,7 @@
 #ifdef STDC_HEADERS
 # include <stdlib.h>	   /* malloc / free */
 # include <ctype.h>		/* isupper / tolower */
+# include <string.h>	/* memset */
 #endif
 
 #ifdef HAVE_MEMORY_H