PR26002 undefined symbol VER_NDX_GLOBAL vs. VER_NDX_LOCAL

PR26002 undefined symbol VER_NDX_GLOBAL vs. VER_NDX_LOCAL

This patch makes undefined unversioned dynamic symbols use
VER_NDX_GLOBAL (version 1) rather than VER_NDX_LOCAL (version 0).
There really isn't much use for an undefined local dynamic symbol, so
we may as well use the logically correct value in .gnu.version.
https://docs.oracle.com/cd/E26505_01/html/E26506/chapter6-54676.html

bfd/
	PR 26002
	* elflink.c (elf_link_output_extsym): Use version 1 in
	.gnu.version for undefined unversioned symbols.
ld/
	PR 26002
	* testsuite/ld-elfvers/vers6.dsym: Expect "Base" for undefined
	unversioned symbols.
	* testsuite/ld-elfvers/vers16.dsym: Likewise.