cmd/compile: correct check for valid -lang version

Change-Id: Iad10d0a2dbc8e12e9f776c6cfb34070f584fd439
Reviewed-on: https://go-review.googlesource.com/c/149057
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/cmd/compile/internal/gc/lang_test.go

@@ -41,6 +41,11 @@ func TestInvalidLang(t *testing.T) {
 		t.Error("compilation with -lang=go9.99 succeeded unexpectedly")
 	}
 
+	// This test will have to be adjusted if we ever reach 1.99 or 2.0.
+	if testLang(t, "go1.99", src, outfile) == nil {
+		t.Error("compilation with -lang=go1.99 succeeded unexpectedly")
+	}
+
 	if testLang(t, "go1.8", src, outfile) == nil {
 		t.Error("compilation with -lang=go1.8 succeeded unexpectedly")
 	}

src/cmd/compile/internal/gc/main.go

@@ -1444,7 +1444,7 @@ func checkLang() {
 		if err != nil {
 			log.Fatalf("internal error parsing default lang %q: %v", def, err)
 		}
-		if langWant.major > defVers.major || (langWant.major == defVers.major && langWant.major > defVers.minor) {
+		if langWant.major > defVers.major || (langWant.major == defVers.major && langWant.minor > defVers.minor) {
 			log.Fatalf("invalid value %q for -lang: max known version is %q", flag_lang, def)
 		}
 	}