C front-end: anonymous struct/union members need not be of struct/union type

A struct or union can contain anonymous members of any type. Code uses
those to ensure a particular layout. Make sure that recursive member
look-up does not try to recurse into types other structs or unions.

Author: tautschnig

regression/ansi-c/anonymous_member1/main.c

@@ -0,0 +1,15 @@
+struct S
+{
+  struct
+  {
+    int : 1;
+    int;
+    int named;
+  };
+};
+
+struct S s = {.named = 0};
+
+int main()
+{
+}

regression/ansi-c/anonymous_member1/test.desc

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

src/ansi-c/anonymous_member.cpp

@@ -88,7 +88,9 @@ bool has_component_rec(
     {
       return true;
     }
-    else if(comp.get_anonymous())
+    else if(
+      comp.get_anonymous() &&
+      (comp.type().id() == ID_struct_tag || comp.type().id() == ID_union_tag))
     {
       if(has_component_rec(comp.type(), component_name, ns))
         return true;