* gdbarch.sh (gcore_bfd_target): New gdbarch callback.

	* gdbarch.h, gdbarch.c: Regenerate.

	* gcore.c (default_gcore_target): Make return value const.
	Call gdbarch_gcore_bfd_target if present.
	(default_gcore_arch, default_gcore_mach): Use target_gdbarch.

	* corelow.c (core_read_description): Call gdbarch_core_read_description
	on core_gdbarch instead of current_gdbarch.

	* ppc-linux-tdep.c (ppc_linux_init_abi): Install gcore_bfd_target.