Add regression test for parsing of enums with underlying type specification

Author: danpoe

regression/ansi-c/enum9/main.c

@@ -0,0 +1,13 @@
+typedef enum : unsigned { X } my_enum1;
+enum my_enum2 : unsigned { Y };
+
+struct S
+{
+  enum my_enum2 : unsigned a;
+  enum my_enum2 : unsigned b: 2;
+};
+
+int main()
+{
+  enum my_enum2 : unsigned enum_var1;
+}

regression/ansi-c/enum9/test.desc

@@ -0,0 +1,7 @@
+CORE
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring