fix the "ANSI C forbids an empty source file" warning.

of course this introduce the "defined but not used" warning.
I'll fix that when later.

dbm/src/memmove.c

@@ -145,3 +145,6 @@ done:
 #endif
 }
 #endif /* no __sgi */
+
+/* Some compilers don't like an empty source file. */
+static int dummy = 0;

dbm/src/snprintf.c

@@ -68,3 +68,6 @@ vsnprintf(str, n, fmt, ap)
 }
 
 #endif /* HAVE_SNPRINTF */
+
+/* Some compilers don't like an empty source file. */
+static int dummy;