C front-end: support storage class and attributes for aggregate objects

Previously we would only support either storage class/type qualifiers _or_ GCC
attributes.

Author: tautschnig

regression/ansi-c/gcc_attributes14/main.c

@@ -0,0 +1,18 @@
+int main()
+{
+  struct S
+  {
+    int x;
+  };
+
+  struct S static __attribute__((__section__(".somewhere")))
+  elements1[] = {{0}};
+
+  struct
+  {
+    int a;
+    int b;
+  } static __attribute__((__section__(".somewhere"))) elements2[] = {{0, 0}};
+
+  return 0;
+}

regression/ansi-c/gcc_attributes14/test.desc

@@ -0,0 +1,8 @@
+CORE gcc-only
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+^CONVERSION ERROR$

src/ansi-c/parser.y

@@ -1172,32 +1172,30 @@ basic_type_specifier:
         }
         ;
 
-/* no gcc type attributes after the following! */
 sue_declaration_specifier:
           declaration_qualifier_list elaborated_type_name
         {
           $$=merge($1, $2);
         }
-        | sue_type_specifier storage_class
+        | sue_type_specifier storage_class gcc_type_attribute_opt
         {
-          $$=merge($1, $2);
+          $$=merge($1, merge($2, $3));
         }
-        | sue_declaration_specifier declaration_qualifier
+        | sue_declaration_specifier declaration_qualifier gcc_type_attribute_opt
         {
-          $$=merge($1, $2);
+          $$=merge($1, merge($2, $3));
         }
         ;
 
-/* no gcc type attributes after the following! */
 sue_type_specifier:
           elaborated_type_name
         | type_qualifier_list elaborated_type_name
         {
           $$=merge($1, $2);
         }
-        | sue_type_specifier type_qualifier
+        | sue_type_specifier type_qualifier gcc_type_attribute_opt
         {
-          $$=merge($1, $2);
+          $$=merge($1, merge($2, $3));
         }
         ;