Why do I keep getting "Killed: 9" when I run this very basic SQLite3 based C file?

I have this super basic C file:

#include <sqlite3.h>
#include <stdio.h>

int main(void) {

    printf("%s\n", sqlite3_libversion()); 

    return 0;
}

And in the same directory I have sqlite3.h, sqlite3.c and sqlite3ext.h downloaded from the downloads page on sqlite.org.

I then run gcc -c main.c. Then chmod +x main.o. Then ./main.o. And every time I get:

Killed: 9

What am I doing wrong?