elf: Treat undefined version as hidden

elf: Treat undefined version as hidden

Since undefined version can't be used to resolve any references without
the original definition, treat it as hidden.

bfd/

	PR binutils/28158
	* elf.c (_bfd_elf_get_symbol_version_string): Treat undefined
	version as hidden.

ld/

	PR binutils/28158
	* testsuite/ld-elf/linux-x86.exp: Run PR binutils/28158 tests.
	* testsuite/ld-elf/pr28158-1.c: New file.
	* testsuite/ld-elf/pr28158-2.S: Likewise.
	* testsuite/ld-elf/pr28158.nd: Likewise.
	* testsuite/ld-elf/pr28158.rd: Likewise.
	* testsuite/ld-elf/pr28158.t: Likewise.
	* testsuite/ld-elfvers/vers2.dsym: Updated.
	* testsuite/ld-elfvers/vers3.dsym: Likewise.
	* testsuite/ld-elfvers/vers6.dsym: Likewise.
	* testsuite/ld-elfvers/vers19.dsym: Likewise.
	* testsuite/ld-elfvers/vers22.dsym: Likewise.
	* testsuite/ld-elfvers/vers23.dsym: Likewise.
	* testsuite/ld-elfvers/vers23d.dsym: Likewise.
	* testsuite/ld-elfvers/vers27d4.dsym: Likewise.
	* testsuite/ld-elfvers/vers28c.dsym: Likewise.