Include the error in the detailed error message in the GCC handler

test/handler/test_gcc_handler.vader

@@ -174,6 +174,22 @@ Execute(The GCC handler should handle notes with no previous message):
   \   '<stdin>:1:1: note: x',
   \ ])
 
+Execute(The GCC handler should attach notes to previous messages):
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 6,
+  \     'col': 12,
+  \     'type': 'E',
+  \     'text': 'Some error',
+  \     'detail': "Some error\n<stdin>:1:1: note: x",
+  \   },
+  \ ],
+  \ ale#handlers#gcc#HandleGCCFormatWithIncludes(347, [
+  \   '-:6:12: error: Some error',
+  \   '<stdin>:1:1: note: x',
+  \ ])
+
 Execute(The GCC handler should interpret - as being the current file):
   AssertEqual
   \ [