static variable initialization in C

I was disappointed to learn recently that C does not allow assignment of variables during static variable initialization, unlike C++. E.g. the following code compiles as C++...

#include <stdio.h>

int foo()
{
  return 1;
}

static int g_i = foo();

int main( int argc, char* argv[] )
{
  printf( "%d\n", g_i );
  return 0;
}

...but issues the following error with a C compiler:

>cc -g main.c
main.c:8:1: error: initializer element is not constant
 static int g_i = foo();
 ^

I thought I could be clever by using the comma operator a-la:

static int g_i = ( foo(), 1 );

...but the compiler seemed unimpressed with my attempted cleverness, and output effectively the same error:

>cc -c main.c
main.c:8:1: error: initializer element is not constant
 static int g_i = ( foo(), 1 );
 ^ 

:(

Q: Why does use of the comma operator not work? I may be unaware of some subtlety, but my understanding led me to think it should have worked: the C compiler is demanding g_i be initialzed to a compiletime constant; supposedly the comma operator would have offered me evaluation of the code left of the comma, but assignment of the code right of the comma, which is a compiletime constant.

Q: Are there any hacks - I don't care how dirty - that would allow assignment to g_i the return value of foo() to g_i?

This is a simplified representation of a C program where I really just want to call a function before main() - I don't care about the return value, but it's a more complicated problem to call a void function before main(), which I would rather sidestep altogether by using an int function whose value is assigned to a throwaway static int variable.