PR22471, undefined reference to linker-defined symbols

PR22471, undefined reference to linker-defined symbols

This patch processes linker script assignment statements before ld
opens DT_NEEDED libraries, in order to define symbols like __bss_start
that might also be defined by a library, falsely triggering an error
about "DSO missing from command line".

The initial value won't be correct when assigning a symbol from dot,
and I make no attempt to handle all expressions.  For example, an
assignment like "_start_foo = ADDR (.foo)" isn't valid until sections
are laid out, so won't define _start_foo early.  What's here should be
enough for most common scripts, and hopefully won't perturb fragile
scripts.

bfd/
	PR 22471
	* elflink.c (_bfd_elf_merge_symbol): Allow weak symbols to override
	early passes over linker script symbols.
	* linker.c (_bfd_generic_link_add_one_symbol): Allow symbols to
	override early passes over linker script symbols.  Clear ldscript_def
	on symbol definitions.
ld/
	PR 22471
	* ldexp.c (struct definedness_hash_entry): Delete "by_script".  Make
	"iteration" an 8-bit field, and update mask in all uses.
	(definedness_newfunc): Don't init "by_script".
	(update_definedness): Test ldscript_def rather than by_script.
	(is_sym_value): Likewise.
	(fold_name <DEFINED>): Return a result for first phase.  Test
	ldscript_def.
	(fold_name <NAME>): Return a result for first phase.
	* ldlang.c (open_input_bfds): Process all assignments, not just
	defsym.
	(lang_process): Increment lang_statement_iteration before
	open_input_bfds.
	* testsuite/ld-mips-elf/tlsdyn-o32-1.d: Adjust for larger .dynsym.
	* testsuite/ld-mips-elf/tlsdyn-o32-1.got: Likewise.
	* testsuite/ld-mips-elf/tlsdyn-o32-2.d: Likewise.
	* testsuite/ld-mips-elf/tlsdyn-o32-2.got: Likewise.
	* testsuite/ld-mips-elf/tlsdyn-o32-3.d: Likewise.
	* testsuite/ld-mips-elf/tlsdyn-o32-3.got: Likewise.