in general generate direct references to the system libraries.

Instead, the build process generates an object file using dynamic
linkage to the desired libraries. The main function is provided by
_cgo_main.c:

	int main() { return 0; }
	void crosscall2(void(*fn)(void*), void *a, int c, uintptr_t ctxt) { }
	uintptr_t _cgo_wait_runtime_init_done(void) { return 0; }
	void _cgo_release_context(uintptr_t ctxt) { }