configure.ac: Set ABI_TWEAKS_SRCDIR.

	* configure.ac: Set ABI_TWEAKS_SRCDIR.
	* configure.host: Set abi_tweaks_dir.  Check for atomicity.h when
	setting atomicity_dir.  Override type_cpu for arm based targets.
	* include/Makefile.am (host_headers): Add cxxabi_tweaks.h.
	* libsupc++/cxxabi.h: Include bits/cxxabi.h. Don't declare __guard.
	* libsupc++/guard.cc: Use definitions from cxxabi_tweaks.h.
	* libsupc++/vec.cc: Ditto.
	* config/cpu/arm/cxxabi_tweaks.h: New file.
	* config/cpu/generic/cxxabi_tweaks.h: New file.
	* */Makefile.in: Regenerate.
	* configure: Regenerate.

From-SVN: r84032