re PR c++/41774 (ice: vector VEC(visibility,base) pop domain error, in pop_visibility at c-pragma.c:757)

	PR c++/41774
	* c-pragma.c (visstack): Change into vector of ints rather than
	enum symbol_visibility.
	(push_visibility): Add kind argument, push default_visibility together
	with kind.
	(pop_visibility): Add kind argument, return true if successful, fail
	if visibility stack is empty or if stack top is of different kind.
	(handle_pragma_visibility): Don't check length of visstack, instead
	call pop_visibility and issue diagnostics if it failed.  Pass 0
	as last argument to push_visibility and pop_visibility.
	* c-pragma.h (push_visibility): Add kind argument.
	(pop_visibility): Likewise.  Return bool instead of void.

	* name-lookup.c (handle_namespace_attrs): Pass 1 as last argument to
	push_visibility.
	* parser.c (cp_parser_namespace_definition): Pass 1 as argument to
	pop_visibility.
	* rtti.c (push_abi_namespace): Pass 2 as last argument to
	push_visibility.
	(pop_abi_namespace): Pass 2 as argument to pop_visibility.

	* g++.dg/ext/visibility/namespace3.C: New test.

From-SVN: r153805