gimple-fold/fab: Move ASSUME_ALIGNED handling to gimple-fold [PR121762]

gimple-fold/fab: Move ASSUME_ALIGNED handling to gimple-fold [PR121762]

This is the next patch in the series of removing fab.
This one is simplier than builtin_constant_p because the only
time we want to simplify this builtin is at the final folding step.

Note align-5.c needs to change slightly as __builtin_assume_aligned
is no longer taken into account for the same reason as why PR 111875
is closed as invalid and why the testcase is failing at -Og
I added a new testcase align-5a.c where the pointer is explictly aligned
so that the check is gone there.
Note __builtin_assume_aligned should really be instrumented for UBSAN,
I filed PR 122038 for that.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/121762
gcc/ChangeLog:

	* gimple-fold.cc (gimple_fold_builtin_assume_aligned): New function.
	(gimple_fold_builtin): Call gimple_fold_builtin_assume_aligned
	for BUILT_IN_ASSUME_ALIGNED.
	* tree-ssa-ccp.cc (pass_fold_builtins::execute): Remove handling
	of BUILT_IN_ASSUME_ALIGNED.

gcc/testsuite/ChangeLog:

	* c-c++-common/ubsan/align-5.c: Update as __builtin_assume_aligned
	is no longer taked into account.
	* c-c++-common/ubsan/align-5a.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>