* elflink.h (elf_merge_symbol): Add one argument to indicate if
a symbol should be skipped. Ignore definitions in dynamic
objects for symbols with non-default visibility.
(elf_add_default_symbol): Adjusted.
(elf_link_add_object_symbols): Check if a symbol should be
skipped. Don't merge the visibility field with the one from
a dynamic object.
(elf_link_check_versioned_symbol): Use undef_bfd.
(elf_link_output_extsym): Warn if a forced local symbol is
referenced from dynamic objects. Make non-weak undefined symbol
with non-default visibility a fatal error.