Add -fipa-cp-alignment

Add -fipa-cp-alignment

This patch adds -fipa-cp-alignment to provide a way to enable/disable
alignment discovery and propagation in IPA-CP.

gcc/

	* common.opt (fipa-cp-alignment): New.
	* ipa-cp.c (ipcp_store_alignment_results): Check
	flag_ipa_cp_alignment.
	* opts.c (default_options_table): Enable -fipa-cp-alignment for
	-O2.
	(enable_fdo_optimizations): Set x_flag_ipa_cp_alignment.
	* doc/invoke.texi: Document -fipa-cp-alignment.

gcc/testsuite/

	* gcc.dg/ipa/propalign-3.c: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@220773 138bc75d-0d04-0410-961f-82ee72b054a4