[C/C++, OpenACC] Reject vars of different scope in acc declare (PR94120)

[C/C++, OpenACC] Reject vars of different scope in acc declare (PR94120)

	gcc/c/
	PR middle-end/94120
	* c-decl.c (c_check_in_current_scope): New function.
	* c-tree.h (c_check_in_current_scope): Declare it.
	* c-parser.c (c_parser_oacc_declare): Add check that variables
	are declared in the same scope as the directive. Fix handling
	of namespace vars.

	gcc/cp/
	PR middle-end/94120
	* paser.c (cp_parser_oacc_declare): Add check that variables
	are declared in the same scope as the directive.

	gcc/testsuite/
	PR middle-end/94120
	* c-c++-common/goacc/declare-pr94120.c: New.
	* g++.dg/declare-pr94120.C: New.

	libgomp/testsuite/
	PR middle-end/94120
	* libgomp.oacc-c++/declare-pr94120.C: New.