[AArch64] Fix TBAA information when lowering NEON loads and stores to gimple

[AArch64] Fix TBAA information when lowering NEON loads and stores to gimple

This patch fixes the wrong TBAA information when lowering NEON loads and stores
to gimple that showed up when bootstrapping with UBSAN.

gcc/ChangeLog:

	* config/aarch64/aarch64-builtins.c
	(aarch64_general_gimple_fold_builtin): Change pointer alignment and
	alias.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/simd/lowering_tbaa.c: New test.