elf: Add -z unique-symbol to avoid duplicated local symbol names

elf: Add -z unique-symbol to avoid duplicated local symbol names

The symbol string table in the .symtab section is optional and cosmetic.
The contents of the .symtab section have no impact on run-time execution.
The symbol names in the symbol string table help distinguish addresses at
different locations.  Add a linker option, -z unique-symbol, to avoid
duplicated local symbol names in the symbol string table.

This feature was well received by the livepatch maintainers.  It not only
solves the duplicated local symbol name problem, but also would allow
livepatch to more precisely locate duplicate symbols in general for
patching.

bfd/

	PR ld/26391
	* elflink.c (elf_final_link_info): Add local_hash_table.
	(local_hash_entry): New.
	(local_hash_newfunc): Likewise.
	(elf_link_output_symstrtab): Append ".COUNT" to duplicated local
	symbols.
	(bfd_elf_final_link): Initialize and free local_hash_table for
	"-z unique-symbol".

include/

	PR ld/26391
	* bfdlink.h (bfd_link_info): Add unique_symbol.

ld/

	PR ld/26391
	* NEWS: Mention "-z unique-symbol".
	* emultempl/elf.em (gld${EMULATION_NAME}_handle_option): Handle
	"-z unique-symbol" and "-z nounique-symbol".
	* ld.texi: Document "-z unique-symbol" and "-z nounique-symbol".
	* lexsup.c (elf_static_list_options): Add "-z unique-symbol" and
	"-z nounique-symbol".
	* testsuite/ld-elf/elf.exp: Add PR ld/26391 tests.
	* testsuite/ld-elf/pr26391.nd: New file.
	* testsuite/ld-elf/pr26391.out: Likewise.
	* testsuite/ld-elf/pr26391a.c: Likewise.
	* testsuite/ld-elf/pr26391b.c: Likewise.
	* testsuite/ld-elf/pr26391c.c: Likewise.
	* testsuite/ld-elf/pr26391d.c: Likewise.