compiler: properly inline methods, use receiver

Notice that this doesn't differentiate between (*T) and (T) receivers always
treating them as is. But we have the same problem with arguments now and the
number of inlined calls is limited, usually we want this behavior.

pkg/compiler/testdata/inline/inline.go

@@ -46,3 +46,13 @@ func SumVar(a, b int) int {
 func Concat(n int) int {
 	return n*100 + b.A*10 + A
 }
+
+type T struct {
+	N int
+}
+
+func (t *T) Inc(i int) int {
+	n := t.N
+	t.N += i
+	return n
+}