#line 1 "not-str-lit"
	void __cgo_f_1_5(void) { static const char __cgo_undefined__5[] = (foo); }

This program will not compile, but cgo can use the presence or absence
of an error message on a given line to deduce the information it
needs. The program is syntactically valid regardless of whether each
name is a type or an ordinary identifier, so there will be no syntax

	// We used to look at specific warning or error messages here, but that tied the
	// behavior too closely to specific versions of the compilers.
	// Instead, arrange that we can infer what we need from only the presence or absence
	// of an error on a specific line.
	//
	// For each name, we generate these lines, where xxx is the index in toSniff plus one.
	//
	//	#line xxx "not-declared"