add test for sketch with extern C func declaration

Signed-off-by: Martino Facchin <[email protected]>

Author: facchinm

Diff for: src/arduino.cc/builder/test/sketch_with_externC/sketch_with_externC.ino

@@ -0,0 +1,11 @@
+void setup() {
+  // put your setup code here, to run once:
+  test();
+}
+
+void loop() {
+  // put your main code here, to run repeatedly:
+
+}
+
+extern "C" void test() {}

Diff for: src/arduino.cc/builder/test/try_build_of_problematic_sketch_test.go

@@ -191,6 +191,10 @@ func TestTryBuild036(t *testing.T) {
 	tryBuildWithContext(t, context, "sketch11", "sketch_fastleds.ino")
 }
 
+func TestTryBuild037(t *testing.T) {
+	tryBuild(t, "sketch_with_externC", "sketch_with_externC.ino")
+}
+
 func makeDefaultContext(t *testing.T) map[string]interface{} {
 	DownloadCoresAndToolsAndLibraries(t)