Add tests for invalid ifeq
diff --git a/test/err_invalid_ifeq2.mk b/test/err_invalid_ifeq2.mk
new file mode 100644
index 0000000..efbdba1
--- /dev/null
+++ b/test/err_invalid_ifeq2.mk
@@ -0,0 +1 @@
+ifeq (