Add support for linking ARMv8-M object files

Add support for linking ARMv8-M object files

2015-12-24  Thomas Preud'homme  <thomas.preudhomme@arm.com>

bfd/
    * elf32-arm.c (using_thumb_only): Check that profile is 'M' and update
    logic around Tag_CPU_arch values to return TRUE for ARMv8-M
    architectures.
    (tag_cpu_arch_combine): Define v8m_baseline and v8m_mainline and update
    v4t_plus_v6_m and comb to deal with ARMv8-M Tag_CPU_arch merging logic.
    (elf32_arm_merge_eabi_attributes): Add Tag_CPU_name values for
    ARMv8-M.

bfd/testsuite/
    * ld-arm/arm-elf.exp (armeabitests_common): Run new tests
    "Thumb-Thumb farcall v8-M", "EABI attribute merging 8",
    "EABI attribute merging 9" and "EABI attribute merging 10".
    (Thumb-Thumb farcall v8-M): Renamed to ...
    (Thumb-Thumb farcall v8-M Mainline): This.
    (Thumb-Thumb farcall v8-M Baseline): New test.
    * ld-arm/attr-merge-8a.s: New file.
    * ld-arm/attr-merge-8b.s: Likewise.
    * ld-arm/attr-merge-8.attr: Likewise.
    * ld-arm/attr-merge-9a.s: Likewise.
    * ld-arm/attr-merge-9b.s: Likewise.
    * ld-arm/attr-merge-9.out: Likewise.
    * ld-arm/attr-merge-10a.s: Likewise.
    * ld-arm/attr-merge-10b.s: Likewise.
    * ld-arm/attr-merge-10.attr: Likewise.