arm: Use REG_CFA_REGISTER instead of UNSPEC_STACK_ALIGN.

arm: Use REG_CFA_REGISTER instead of UNSPEC_STACK_ALIGN.

This requires a bit of extra preparation in arm_unwind_emit, in
order to handle the change for ARM unwinding.

        * config/arm/arm.c (arm_dwarf_handle_frame_unspec): Remove.
        (TARGET_DWARF_HANDLE_FRAME_UNSPEC): Remove.
        (arm_expand_prologue): Use REG_CFA_REGISTER to mark the
        stack pointer save.
        (arm_unwind_emit_set): Don't recognize UNSPEC_STACK_ALIGN.
        (arm_unwind_emit): Walk REG_NOTES for unwinding notes.  Emit
        proper unwind info for a REG_CFA_REGISTER save of stack pointer.
        * config/arm/arm.md (UNSPEC_STACK_ALIGN): Remove.

From-SVN: r175870