Restore readelf -wF

Commit 94585d6d4495 resulted in readelf -wF failing with
Unrecognized debug letter option 'F'

binutils/
	* dwarf.c (debug_dump_long_opts): Add letter.
	(debug_option_table): New, replacing..
	(opts_table, letter_table): ..these.
	(dwarf_select_sections_by_names): Adjust to suit.  Set
	do_debug_frames outside of loop.
	(dwarf_select_sections_by_letters): Similarly.
gas/
	* testsuite/gas/i386/ehinterp.d: Use readelf -wF.