c++: Fix up ICE in emit_support_tinfo_1 [PR109042]

c++: Fix up ICE in emit_support_tinfo_1 [PR109042]

In my recent rtti.cc change I assumed when emitting the support tinfos
that the tinfos for the fundamental types haven't been created yet.
Normally (in libsupc++.a (fundamental_type_info.o)) that is the case,
but as can be seen on the testcase, one can violate it by using typeid
etc. in the same TU and do it before ~__fundamental_type_info ()
definition.

The following patch fixes that by popping from unemitted_tinfo_decls
only in the normal case when it is there, and treating non-NULL
DECL_INITIAL on a tinfo node as indication that emit_tinfo_decl has
processed it already.

2023-03-07  Jakub Jelinek  <jakub@redhat.com>

	PR c++/109042
	* rtti.cc (emit_support_tinfo_1): Don't assert that last
	unemitted_tinfo_decls element is tinfo, instead pop from it only in
	that case.
	* decl2.cc (c_parse_final_cleanups): Don't call emit_tinfo_decl
	for unemitted_tinfO_decls which have already non-NULL DECL_INITIAL.

	* g++.dg/rtti/pr109042.C: New test.