cgo: implement support for static functions

testdata/cgo/extra.go

@@ -3,4 +3,18 @@ package main
 // Make sure CGo supports multiple files.
 
 // int fortytwo(void);
+// static float headerfunc_static(float a) { return a - 1; }
+// static void headerfunc_void(int a, int *ptr) { *ptr = a; }
 import "C"
+
+func headerfunc_2() {
+	// Call headerfunc_static that is different from the headerfunc_static in
+	// the main.go file.
+	// The upstream CGo implementation does not handle this case correctly.
+	println("static headerfunc 2:", C.headerfunc_static(5))
+
+	// Test function without return value.
+	var n C.int
+	C.headerfunc_void(3, &n)
+	println("static headerfunc void:", n)
+}