elf: Handle .gnu.debuglto_.debug_* sections

commit 994b2513
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Sun Jan 17 20:01:16 2021 -0800

    ld/elf: Ignore section symbols when matching linkonce with comdat

ignored section symbols when comparing symbols in 2 sections.  Since all
references to debugging sections are done with section symbols, symbols
in debugging sections are ignored and we fail to match symbols in comdat
debugging sections.  Also .gnu.debuglto_.debug_* sections aren't treated
as debugging sections.

1. Treate .gnu.debuglto_.debug_ section as debugging section unless it
is marked with SHF_EXCLUDE.
2. Revert commit 994b2513 in elf_create_symbuf.
3. Ignore section symbols only when matching non-debugging sections or
linkonce section with comdat section.

bfd/

	PR ld/27590
	* elf.c (_bfd_elf_make_section_from_shdr): Treate
	.gnu.debuglto_.debug_ section as debugging section unless it is
	marked with SHF_EXCLUDE.
	* elflink.c (elf_create_symbuf): Revert commit 994b2513.
	(bfd_elf_match_symbols_in_sections): Ignore section symbols when
	matching non-debugging sections or linkonce section with comdat
	section.

ld/

	PR ld/27590
	* testsuite/ld-elf/pr27590.s: New file.
	* testsuite/ld-elf/pr27590a.d: Likewise.
	* testsuite/ld-elf/pr27590b.d: Likewise.
	* testsuite/ld-i386/i386.exp: Also run ld/27193 test with
	--reduce-memory-overheads.