c++: Fix ICE due to folding a call to constructor on cdtor_returns_this arches...

c++: Fix ICE due to folding a call to constructor on cdtor_returns_this arches (aka arm32) [PR113083]

When targetm.cxx.cdtor_returns_this () (aka on arm32 TARGET_AAPCS_BASED)
constructor is supposed to return this pointer, but when we cp_fold such
a call, we don't take that into account and just INIT_EXPR the object,
so we can later ICE during gimplification, because the expression doesn't
have the right type.

2024-02-23  Jakub Jelinek  <jakub@redhat.com>

	PR c++/113083
	* cp-gimplify.cc (cp_fold): For targetm.cxx.cdtor_returns_this ()
	wrap r into a COMPOUND_EXPR and return folded CALL_EXPR_ARG (x, 0).

	* g++.dg/cpp0x/constexpr-113083.C: New test.