c-family: Copy DECL_USER_ALIGN even if DECL_ALIGN is similar.

c-family: Copy DECL_USER_ALIGN even if DECL_ALIGN is similar.

When re-declaring a function with differing attributes DECL_USER_ALIGN
is usually not merged/copied when DECL_ALIGN is similar.  On s390 this
will cause a warning message not to be shown.  Similarly, we warned
about the wrong alignment when short-circuiting an alignment initialization in
common_handle_aligned_attribute ().

Fix this by copying DECL_USER_ALIGN even if DECL_ALIGN is similar as
well as getting rid of the short-circuited initialization.

gcc/c-family/ChangeLog:

	* c-attribs.c (common_handle_aligned_attribute): Remove short
	circuit and dead code.

gcc/c/ChangeLog:

	* c-decl.c (merge_decls): Copy DECL_USER_ALIGN if DECL_ALIGN is
	similar.

gcc/cp/ChangeLog:

	* decl.c (duplicate_decls): Likewise.