c++: ICE with bad definition of decimal32 [PR100261]

The change to only look at the global binding for non-classes meant that
here, when dealing with decimal32 which is magically mangled like its first
non-static data member, we got a collision with the mangling for float.
Fixed by also looking up an existing binding for such magical classes.

	PR c++/100261

gcc/cp/ChangeLog:

	* rtti.c (get_tinfo_decl_direct): Check TYPE_TRANSPARENT_AGGR.

gcc/testsuite/ChangeLog:

	* g++.dg/dfp/mangle-6.C: New test.

gcc/cp/rtti.c

@@ -433,7 +433,7 @@ get_tinfo_decl_direct (tree type, tree name, int pseudo_ix)
   if (!name)
     name = mangle_typeinfo_for_type (type);
 
-  if (!CLASS_TYPE_P (type))
+  if (!CLASS_TYPE_P (type) || TYPE_TRANSPARENT_AGGR (type))
     d = get_global_binding (name);
 
   if (!d)

gcc/testsuite/g++.dg/dfp/mangle-6.C

@@ -0,0 +1,19 @@
+// PR c++/100261
+// { dg-do compile }
+
+#include <typeinfo>
+
+namespace std {
+  namespace decimal {
+    class decimal32 {
+      float private__decfloat32;
+    };
+  }
+}
+
+void
+foo ()
+{
+  typeid (float);
+  typeid (std::decimal::decimal32);
+}