Add noreturn attributes and remove unreachable code.

	Add noreturn attributes and remove unreachable code.

	* grub-core/bus/cs5536.c (grub_cs5536_smbus_wait): Remove unreachable
	code.
	* grub-core/commands/halt.c (grub_cmd_halt): Remove unreachable
	code. Mark as noreturn.
	* grub-core/commands/minicmd.c (grub_mini_cmd_exit): Likewise.
	* grub-core/commands/reboot.c (grub_cmd_reboot): Likewise.
	* grub-core/disk/efi/efidisk.c (grub_efidisk_get_device_name): Remove
	unreachable code.
	* grub-core/kern/main.c (grub_main): Mark as noreturn.
	* grub-core/kern/rescue_reader.c (grub_rescue_run): Likewise.
	* grub-core/lib/posix_wrap/stdlib.h (abort): Likewise.
	* grub-core/normal/menu.c (run_menu): Remove unreachable code.
	* include/grub/kernel.h (grub_main): Mark as noreturn.
	* include/grub/reader.h (grub_rescue_run): Likewise.