Initial patch to enable gold aarch64 backend.
This patch is just a skeleton which almost does nothing.
It does not support ILP32 now.
gold/ChangeLog:
* aarch64.cc: New file
* Makefile.am (TARGETSOURCES): Add aarch64.cc
(ALL_TARGETOBJS): Add aarch64.$(OBJEXT)
* Makefile.in: Regenerate.
* configure.tgt: Add entries for aarch64*.
* configure.ac: Likewise.
* configure: Likewise.
elfcpp/ChangeLog:
* aarch64.h: New file. New enums for aarch64-elf64 relocations.
* elfcpp.h (EM_AARCH64, SHT_AARCH64_ATTRIBUTES, PT_AARCH64_ARCHEXT,
PT_AARCH64_UNWIND): New enum constant.
Jing Yu