[gold][aarch64]: Erratum 843419 optimized fix

[Han Shen]

Hi Cary, this is the patch for erratum 843419 fix optimization.

Usually we apply branch-to-stub fix for all erratum. For 843419, under some
condition, instead of generating jumps, we re-write 'adrp' with 'adr' (only
applicable if adrp calculation result fits in adr range), thus break such
erratum sequence and eliminate performance penalty (2-jump/fix).

Test - build on x86_64 platform and aarch64 platform using opt and debug (-O0).
  Pass unit tests.  Pass gold local test suite.  Pass tests from arm.

Ok for trunk?

gold/ChangeLog

2015-07-15 Han Shen <shenhan@google.com>

        Optimize erratum 843419 fix.

        gold/ChangeLog: * aarch64.cc (AArch64_insn_utilities::is_adr): New
        method.  (AArch64_insn_utilities::aarch64_adr_encode_imm): New method.
        (AArch64_insn_utilities::aarch64_adrp_decode_imm): New method.
        (E843419_stub): New sub-class of Erratum_stub.
        (AArch64_relobj::try_fix_erratum_843419_optimized): New method.
        (AArch64_relobj::section_needs_reloc_stub_scanning): Try optimized fix.
        (AArch64_relobj::create_erratum_stub): Add 1 argument.
        (Target_aarch64::scan_erratum_843419_span): Pass in adrp insn offset.

-- 
Han Shen
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