A new vendor CFA DW_CFA_AARCH64_negate_ra_state was introduced for ARMv8.3-A
return address signing, it is multiplexing DW_CFA_GNU_window_save in CFA vendor
extension space.

  This patch adds necessary code to make it available to external, the GDB
patch (https://sourceware.org/ml/gdb-patches/2017-08/msg00215.html) is intended
to use it.

  A new DW_CFA_DUP for it is added in dwarf2.def.  The use of DW_CFA_DUP is to
avoid duplicated case value issue when included in libiberty/dwarfnames.

  Native x86 builds OK to make sure no macro expanding errors.

Committed on behalf of Jiong Wang.

    include/
	* dwarf2.def (DW_CFA_AARCH64_negate_ra_state): New DW_CFA_DUP.
	* dwarf2.h (DW_CFA_DUP): New define.

    libiberty/
	* dwarfnames.c (DW_CFA_DUP): New define.

From-SVN: r252037