change default zeta_C compiler to gcc & complete 10815.c

zeta_C/14425.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main() {
+    int N, M;
+    char[]
+    scanf("%d %d", &N, &M);
+
+
+    return 0;
+}