静态变量和静态函数如何声明?vs和gcc中编译差异

代码如下:
#include<stdio.h>
//#pragma warning(disable:4996)
extern int a;
extern void func();
int main()
{
func();
printf("%d\n", a);
return 0;
}
static int a = 100;
static void func()
{
printf("func()\n");
}
viual studio编译过了
gcc编译失败,报错
static declaration of 'a' follows non-static declaration
大佬知道怎么声明静态变量和静态函数吗