varasm.c (merge_weak): Error for any weakening after definition.

varasm.c (merge_weak): Error for any weakening after definition.

        * varasm.c (merge_weak): Error for any weakening after definition.
        Adjust weakening after use warning to catch more cases.
        (assemble_alias): Set TREE_USED and TREE_ASM_WRITTEN consistently.
        * config/alpha/alpha.c (alpha_encode_section_info): Do not abort.

        * gcc.dg/weak-5.c (vfoo1c): No warning here.
        (vfoo1f): Warning here.
        (vfoo1l): Don't redefine the alias.

From-SVN: r53491