Update to 2.31.1

Changelog:
2.31.1
  This release also contains a fix for PR gold/23409 where the gold
  linker could end up creating duplicate copies of some symbols.

2.31
This release contains numerous bug fixes, and also the
following new features:

  * Direct linking with DLLs for Cygwin and Mingw targets is now faster.

  * The linker now defaults to enabling -z separate-code for Linux
    targets, although a configure time option can change this.
    This option can increase disk and memory size of executables, but
    it does help to improve security.

  * The disassembler supports Netronome Flow Processor (NFP) firmware
    files.

  * The AArch64 disassembler supports showing disassembly notes which
    are emitted when inconsistencies are found with the instruction that
    may result in the instruction being invalid.  It also emits warnings
    when a combination of an instruction and a named register could be
    invalid.

  * The AR archive manager now supports an "O" modifier to display
    member offsets inside an archive.

  * The ADR and ADRL pseudo-instructions supported by the ARM assembler
    now only set the bottom bit of the address of thumb function symbols
    if the -mthumb-interwork command line option is active.

  * The MIPS assembler supports the Global INValidate (GINV) and
    Cyclic Redudancy Check (CRC) architecture extensions.

  * Support has been added for the Freescale S12Z architecture.

  * The assembler has a new --generate-missing-build-notes=[yes|no]
    option to create (or not) GNU Build Attribute notes if none are
    present in the input sources.

  * The -mold-gcc command-line option has been removed for x86 targets.

  * The x86 assembler now supports a -O[2|s] command-line options to
    enable alternate shorter instruction encodings.

  * The gold linker has a new --debug=plugin option for easier debugging
    of plugin-related problems.

  * The gold linker now supports the -z keep_text_section_prefix option.

  * The gold linker now has support for .note.gnu.property sections
    (from Linux ABI extensions).

  * Add gold linker now has support for Intel's Indirect Branch Tracking
    (IBT) and Shadow Stack instructions.

(ryoon)