elf: Don't set its DT_VERSYM entry for unversioned symbol

elf: Don't set its DT_VERSYM entry for unversioned symbol

1. Referenced symbol without '@' has no version.
2. Defined symbol without the .symver directive has no version if there
is no linker version script.

Symbol without version shouldn't have the base version in its DT_VERSYM
entry.  Instead, its DT_VERSYM entry should be all zero to indicate that
the symbol doesn't have a version.

NB: Symbol with the base version has a '@' suffix, like "foo@", defined
with

.symver hide_original_foo, foo@

bfd/

	PR ld/33577
	* elflink.c (elf_link_output_extsym): Don't set its DT_VERSYM
	entry for the symbol without version.

ld/

	PR ld/33577
	* ld-elfvers/vers16.dsym: Remove the "Base" version on symbols
	without version.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>