acinclude.m4: Check for <stdalign.h>

	* acinclude.m4: Check for <stdalign.h>
	* configure: Regenerate.
	* config.h.in: Likewise.
	* include/Makefile.am: Add <cstdalign>.
	* include/Makefile.in: Regenerate.
	* include/c_global/cstdalign: New.
	* testsuite/18_support/headers/cstdalign/std_c++0x_neg.cc: New.
	* doc/xml/manual/backwards_compatibility.xml: Update.
	* doc/xml/manual/status_cxx2011.xml: Update.

From-SVN: r181076