libstdc++: fix pointer type exception catch (no RTTI) [PR105387]

__pbase_type_info::__do_catch(), used to catch pointer type exceptions,
did not check if the type info object to compare against is a pointer
type info object before doing a static down-cast to a pointer type info
object. If RTTI is disabled, this leads to the following situation:
Since a pointer type info object has additional fields, they would
end up being undefined if the actual type info object was not a pointer
type info object.

A simple check has been added before the down-cast happens.

Note that a consequence of this check is that exceptions of type
pointer-to-member cannot be caught anymore.

In case RTTI is enabled, this does not seem to be a problem because
RTTI-based checks would run before and prevent running into the bad
down-cast. Hence, the fix is disabled if RTTI is enabled and exceptions
of type pointer-to-member can still be caught.

libstdc++-v3/ChangeLog:

	PR libstdc++/105387
	* libsupc++/pbase_type_info.cc (__do_catch) [!__cpp_rtti]: Add
	check that the thrown type is actually a pointer.
	* testsuite/18_support/105387.cc: New test.
	* testsuite/18_support/105387_memptr.cc: New test.

Signed-off-by: Jakob Hasse <jakob.hasse@espressif.com>