Add signal number conversions for OpenBSD.

gdb/ChangeLog:

        * obsd-tdep.h (obsd_init_abi): New prototype.
        * obsd-tdep.c: Define enum with OpenBSD signal numbers.
        (obsd_gdb_signal_from_target, obsd_gdb_signal_to_target)
        (obsd_init_abi): New functions.
        * i386obsd-tdep.c: Include "obsd-tdep.h".
        (i386obsd_init_abi): Call obsd_init_abi.
        * amd64obsd-tdep.c: Include "obsd-tdep.h".
        (amd64obsd_init_abi): Call obsd_init_abi.
        * configure.tgt (i[34567]86-*-openbsd*, x86_64-*-openbsd*): Add
        obsd-tdep.c to gdb_target_obs.
PR15530, mark symbol in executables if it matches dynamic_list

For powerpc64 as HJ did earlier for other ELF targets, and a tidy.

	PR gold/15530
	* elf64-ppc.c (ppc64_elf_gc_mark_dynamic_ref): Support
	--export-dynamic and --dynamic-list marking of symbols.
	* elflink.c (bfd_elf_gc_mark_dynamic_ref_symbol): Reorder
	cheap tests first.
Enable ppc476 workaround for ld -r.

The Linux kernel builds modules using ld -r.  These might need the
ppc476 workaround, so enable it for ld -r if sections have sufficient
alignment to tell location within a page.

bfd/
	* elf32-ppc.c (ppc_elf_relax_section): Enable ppc476 workaround
	for ld -r, when code sections are sufficiently aligned.
	* elf32-ppc.h (struct ppc_elf_params): Delete pagesize.  Add
	pagesize_p2.
ld/
	* emultempl/ppc32elf.em (pagesize): New static var.
	(ppc_after_open_output): Set params.pagesize_p2 from pagesize.
	(PARSE_AND_LIST_ARGS_CASES): Adjust to use pagesize.
Fix bad interaction between --relax and tls optimisation

Adding long-branch stubs for __tls_get_addr calls that are optimised
away is silly.  It also causes assertion failures on newer object files
that use R_PPC_TLSGD and R_PPC_TLSLD marker relocs, and half-optimised
(ie. broken) code for older object files.

	PR 16546
	* elf32-ppc.c (ppc_elf_relax_section): Don't build long-branch
	stubs for calls to __tls_get_addr that we know will later be
	optimised away.