re PR middle-end/84237 (xen build faiulre only zero initializers are allowed in section '.bss.page_aligned.const')

	PR middle-end/84237
	* output.h (bss_initializer_p): Add NAMED argument, defaulted to false.
	* varasm.c (bss_initializer_p): Add NAMED argument, if true, ignore
	TREE_READONLY bit.
	(get_variable_section): For decls in named .bss* sections pass true as
	second argument to bss_initializer_p.

	* gcc.dg/pr84237.c: New test.

From-SVN: r257513