PR100281 C++: Fix SImode pointer handling

PR100281 C++: Fix SImode pointer handling

The problem appears to be triggered by two locations in the front-end
where non-POINTER_SIZE pointers aren't handled right now.

1. An assertion in strip_typedefs is triggered because the alignment
of the types don't match. This in turn is caused by creating the new
type with build_pointer_type instead of taking the type of the
original pointer into account.

2. An assertion in cp_convert_to_pointer is triggered which expects
the target type to always have POINTER_SIZE.

gcc/cp/ChangeLog:

	PR c++/100281
	* cvt.c (cp_convert_to_pointer): Use the size of the target
	pointer type.
	* tree.c (cp_build_reference_type): Call
	cp_build_reference_type_for_mode with VOIDmode.
	(cp_build_reference_type_for_mode): Rename from
	cp_build_reference_type.  Add MODE argument and invoke
	build_reference_type_for_mode.
	(strip_typedefs): Use build_pointer_type_for_mode and
	cp_build_reference_type_for_mode for pointers and references.

gcc/ChangeLog:

	PR c++/100281
	* tree.c (build_reference_type_for_mode)
	(build_pointer_type_for_mode): Pick pointer mode if MODE argument
	is VOIDmode.
	(build_reference_type, build_pointer_type): Invoke
	build_*_type_for_mode with VOIDmode.

gcc/testsuite/ChangeLog:

	PR c++/100281
	* g++.target/s390/pr100281-1.C: New test.
	* g++.target/s390/pr100281-2.C: New test.

(cherry picked from commit 720dff974ea0487c35c0a4bfa527f30df5066ce1)