patch 8.1.1047: WINCH signal is not tested

Problem:    WINCH signal is not tested.
Solution:   Add a test. (Dominique Pelle, closes #4158)
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index c12a59e..8581700 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -224,6 +224,7 @@
 	test_searchpos \
 	test_set \
 	test_sha256 \
+	test_signals \
 	test_signs \
 	test_smartindent \
 	test_sort \
@@ -385,6 +386,7 @@
 	test_scrollbind.res \
 	test_search.res \
 	test_shortpathname.res \
+	test_signals.res \
 	test_signs.res \
 	test_smartindent.res \
 	test_source.res \