This adds support for marking RL78 binaries as either supporting 32-bit

This adds support for marking RL78 binaries as either supporting 32-bit
or 64-bit doubles.  It also makes the linker complain if the user attempts
to link together binaries with different sized doubles.

	* elf32-rl78.c (rl78_elf_merge_private_bfd_data): Complain if
	64-bit doubles objects mix with 32-bit doubles objects.
	(rl78_elf_print_private_bfd_data): Describe 64-bit doubles flag.

	* readelf.c (get_machine_flags): Handle RL78 64-bit doubles flag.

	* config/tc-rl78.c (enum options): Add OPTION_32BIT_DOUBLES
	and OPTION_64BIT_DOUBLES.
	(md_longopts): Add -m32bit-doubles and -m64bit-doubles.
	(md_parse_option): Parse -m32bit-doubles and -m64bit-doubles.
	(md_show_usage): Show all of the RL78 options.
	(rl78_float_cons): New static functions.
	(md_pseudo_table): Update handler for "double".