Remove magic treatment of toc symbols for powerpc ELF

The XCOFF assembler does some wierd things with instructions like
`lwz 9,sym(30'.  See the comment in md_apply_fix.  From an ELF
perspective, it's weird even to magically select a TOC16 reloc
when a symbol is in the TOC/GOT.  ELF assemblers generally use
modifiers like @toc to select relocs, so remove this "feature"
for ELF.  I believe this was to support gcc -m32 -mcall-aixdesc
but that combination of gcc options has been broken for a long
time.

	* config/tc-ppc.c (ppc_is_toc_sym): Remove OBJ_ELF support.
	(md_assemble): Don't call ppc_is_toc_sym for ELF.
Support more relocs on 16-bit insn fields

This patch allows gas to assemble a testcase like
	li 3,ext_sym
which oddly was not accepted while the following is OK:
	li 3,ext_sym@l

	* config/tc-ppc.c (md_assemble): Move code adjusting reloc types
	later.  Merge absolute and relative branch reloc selection.
	Generate 16-bit relocs for most 16-bit insn fields given a
	non-constant expression.
Support R_PPC64_ADDR64_LOCAL

This adds support for "func@localentry", an expression that returns the
ELFv2 local entry point address of function "func".  I've excluded
dynamic relocation support because that obviously would require glibc
changes.

include/elf/
	* ppc64.h (R_PPC64_REL24_NOTOC, R_PPC64_ADDR64_LOCAL): Define.
bfd/
	* elf64-ppc.c (ppc64_elf_howto_raw): Add R_PPC64_ADDR64_LOCAL entry.
	(ppc64_elf_reloc_type_lookup): Support R_PPC64_ADDR64_LOCAL.
	(ppc64_elf_check_relocs): Likewise.
	(ppc64_elf_relocate_section): Likewise.
	* Add BFD_RELOC_PPC64_ADDR64_LOCAL.
	* bfd-in2.h: Regenerate.
	* libbfd.h: Regenerate.
gas/
	* config/tc-ppc.c (ppc_elf_suffix): Support @localentry.
	(md_apply_fix): Support R_PPC64_ADDR64_LOCAL.
ld/testsuite/
	* ld-powerpc/elfv2-2a.s, ld-powerpc/elfv2-2b.s: New files.
	* ld-powerpc/elfv2-2exe.d, ld-powerpc/elfv2-2so.d: New files.
	* ld-powerpc/powerpc.exp: Run new test.
elfcpp/
	* powerpc.h (R_PPC64_REL24_NOTOC, R_PPC64_ADDR64_LOCAL): Define.
gold/
	* powerpc.cc (Target_powerpc::Scan::local, global): Support
	R_PPC64_ADDR64_LOCAL.
	(Target_powerpc::Relocate::relocate): Likewise.
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