* hooks.h (hook_uint_mode_0): Add Prototype.
	* hooks.c (hook_uint_mode_0): New default function.
	* target.def (atomic_align_for_mode): New target hook.
	* tree.c (build_atomic_base): Add alignment override parameter.
	(build_common_tree_nodes): Use atomic alignment override.
	* doc/tm.texi.in (TARGET_ATOMIC_ALIGN_FOR_MODE): Define.
	* doc/tm.texi (TARGET_ATOMIC_ALIGN_FOR_MODE): Add description.

From-SVN: r205273