patch 9.0.1234: the code style has to be checked manually

Problem:    The code style has to be checked manually.
Solution:   Add basic code style checks in a test.  Fix or avoid uncovered
            problems.
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index fdca9f4..f198217 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -97,6 +97,7 @@
 	test_cmdline \
 	test_cmdmods \
 	test_cmdwin \
+	test_codestyle \
 	test_command_count \
 	test_comments \
 	test_comparators \
@@ -359,6 +360,7 @@
 	test_cmdline.res \
 	test_cmdmods.res \
 	test_cmdwin.res \
+	test_codestyle.res \
 	test_command_count.res \
 	test_comments.res \
 	test_comparators.res \