[c] "Unresolved inclusion" error with Eclipse CDT for C standard library headers

I set up CDT for eclipse and wrote a simple hello world C program:

#include <stdio.h>

int main(void){
    puts("Hello, world.");
    return 0;
}

The program builds and runs correctly, but eclipse keeps showing this yellow question mark by the side of inclusion statement that says "Unresolved inclusion: <stdio.h>" when I put mouse over it.

It doesn't affect running of the program but I find it rather annoying.

Does anyone have any idea how to remove it?