c++: Fix ICE with xobj parms and maybe incomplete decl-specifiers

This fixes a null dereference issue when decl_specifiers.type is not yet
provided.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_parameter_declaration): Check if
	decl_specifiers.type is null.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp23/explicit-obj-basic7.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
2 files changed