identifiers C.foo, cgo generates this C program:

	<preamble>
	#line 1 "not-declared"
	void __cgo_f_1_1(void) { __typeof__(foo) *__cgo_undefined__1; }
	#line 1 "not-type"
	void __cgo_f_1_2(void) { foo *__cgo_undefined__2; }
	#line 1 "not-int-const"
	void __cgo_f_1_3(void) { enum { __cgo_undefined__3 = (foo)*1 }; }
	#line 1 "not-num-const"
	void __cgo_f_1_4(void) { static const double __cgo_undefined__4 = (foo); }
	#line 1 "not-str-lit"