patch 8.1.1308: the Normal highlight is not defined when compiled with GUI

Problem:    The Normal highlight is not defined when compiled with GUI.
Solution:   Always define Normal. (Christian Brabandt, closes #4072)
diff --git a/src/testdir/test_highlight.vim b/src/testdir/test_highlight.vim
index e16abf1..24379d6 100644
--- a/src/testdir/test_highlight.vim
+++ b/src/testdir/test_highlight.vim
@@ -572,3 +572,10 @@
   call StopVimInTerminal(buf)
   call delete('Xtest_cursorline_with_visualmode')
 endfunc
+
+func Test_1_highlight_Normalgroup_exists()
+  " This test must come before the Test_cursorline test, as it appears this
+  " defines the Normal highlighting group anyway.
+  let hlNormal = HighlightArgs('Normal')
+  call assert_match('hi Normal\s*clear', hlNormal)
+endfunc