[AArch64][4/4] libgcc unwinder support for return address signing

[AArch64][4/4] libgcc unwinder support for return address signing

libgcc/
	* config/aarch64/aarch64-unwind.h: New file.
	(DWARF_REGNUM_AARCH64_RA_STATE): Define.
	(MD_POST_EXTRACT_ROOT_ADDR): New target marcro and define it on AArch64.
	(MD_POST_EXTRACT_FRAME_ADDR): Likewise.
	(MD_POST_FROB_EH_HANDLER_ADDR): Likewise.
	(MD_FROB_UPDATE_CONTEXT): Define it on AArch64.
	(aarch64_post_extract_frame_addr): New function.
	(aarch64_post_frob_eh_handler_addr): New function.
	(aarch64_frob_update_context): New function.
	* config/aarch64/linux-unwind.h: Include aarch64-unwind.h
	* config.host (aarch64*-*-elf, aarch64*-*-rtems*,
	aarch64*-*-freebsd*):
	Initialize md_unwind_header to include aarch64-unwind.h.
	* unwind-dw2.c (struct _Unwind_Context): Define "RA_A_SIGNED_BIT".
	(execute_cfa_program): Multiplex DW_CFA_GNU_window_save for
	__aarch64__.
	(uw_update_context): Honor MD_POST_EXTRACT_FRAME_ADDR.
	(uw_init_context_1): Honor MD_POST_EXTRACT_ROOT_ADDR.
	(uw_frob_return_addr): New function.
	(uw_install_context): Use uw_frob_return_addr.

From-SVN: r244673