patch 8.1.0594: libvterm tests fail to run on Mac

Problem:    Libvterm tests fail to run on Mac.
Solution:   Only run libvterm tests on Linux.

src/Makefile

@@ -2160,8 +2160,12 @@ run_message_test: $(MESSAGE_TEST_TARGET)
 	$(VALGRIND) ./$(MESSAGE_TEST_TARGET) || exit 1; echo $* passed;
 
 # Run the libvterm tests.
+# This currently doesn't work on Mac, only run on Linux for now.
 test_libvterm:
-	cd libvterm; $(MAKE) -f Makefile test CC="$(CC)"
+	@if test `uname` = "Linux"; then \
+		cd libvterm; $(MAKE) -f Makefile test \
+			CC="$(CC)" CFLAGS="$(CFLAGS)" LDFLAGS="$(LDFLAGS)"; \
+	fi
 
 # Run individual OLD style test.
 # These do not depend on the executable, compile it when needed.

src/version.c

@@ -799,6 +799,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    594,
 /**/
     593,
 /**/