i386/x86-64: Add unwind info for .plt.got section

i386/x86-64: Add unwind info for .plt.got section

When there are both PLT and GOT references to the same function symbol,
linker combines GOTPLT and GOT slots into a single GOT slot and create
an entry in .plt.got section for PLT access via the GOT slot.  This
patch adds unwind info for .plt.got section.

bfd/

	PR ld/20830
	* elf32-i386.c (elf_i386_eh_frame_plt_got): New.
	(PLT_GOT_FDE_LENGTH): Likewise.
	(elf_i386_plt_layout): Add eh_frame_plt_got and
	eh_frame_plt_got_size.
	(elf_i386_plt): Updated.
	(elf_i386_link_hash_table): Add plt_got_eh_frame.
	(elf_i386_check_relocs): Create .eh_frame section for .plt.got.
	(elf_i386_size_dynamic_sections): Allocate and initialize
	.eh_frame section for .plt.got.
	(elf_i386_finish_dynamic_sections): Adjust .eh_frame section for
	.plt.got.
	(elf_i386_nacl_plt): Add FIXME for eh_frame_plt_got and
	eh_frame_plt_got_size.
	* elf64-x86-64.c (elf_x86_64_eh_frame_plt_got): New.
	(PLT_GOT_FDE_LENGTH): Likewise.
	(elf_x86_64_backend_data): Add eh_frame_plt_got and
	eh_frame_plt_got_size.
	(elf_x86_64_arch_bed): Updated.
	(elf_x86_64_bnd_arch_bed): Add FIXME for eh_frame_plt_got and
	eh_frame_plt_got_size.
	(elf_x86_64_nacl_arch_bed): Likewise.
	(elf_x86_64_link_hash_table): Add plt_got_eh_frame.
	(elf_x86_64_check_relocs): Create .eh_frame section for .plt.got.
	(elf_x86_64_size_dynamic_sections): Allocate and initialize
	.eh_frame section for .plt.got.
	(elf_x86_64_finish_dynamic_sections): Adjust .eh_frame section
	for .plt.got.

ld/

	PR ld/20830
	* testsuite/ld-i386/i386.exp: Run pr20830.
	* testsuite/ld-x86-64/x86-64.exp: Likewise.
	* testsuite/ld-i386/pr20830.d: New file.
	* testsuite/ld-i386/pr20830.s: Likewise.
	* testsuite/ld-x86-64/pr20830.d: Likewise.
	* testsuite/ld-x86-64/pr20830.s: Likewise.