dwarf: Also match abbrev base when searching abbrev list

dwarf: Also match abbrev base when searching abbrev list

A .debug_abbrev section can have multiple CUs.  When caching abbrev list,
we need to check abbrev base to support multiple CUs.

	PR binutils/26808
	* dwarf.c (abbrev_list): Add abbrev_base.
	(new_abbrev_list): Add an abbrev_base argument and record it.
	(find_abbrev_list_by_abbrev_offset): Add an abbrev_base argument
	and match it.
	(process_debug_info): Pass abbrev_base to new_abbrev_list and
	find_abbrev_list_by_abbrev_offset.
	(display_debug_abbrev): Pass 0 abbrev_base to new_abbrev_list
	and find_abbrev_list_by_abbrev_offset.
	* testsuite/binutils-all/x86-64/pr26808.dump: New file.
	* testsuite/binutils-all/x86-64/pr26808.dwp.bz2: Likewise.
	* testsuite/binutils-all/x86-64/x86-64.exp: Run PR binutils/26808
	test.