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

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.