Add a warning if an emtpty SHT_REL, SHT_RELA or SHT_PROGBITS section is detected...

Add a warning if an emtpty SHT_REL, SHT_RELA or SHT_PROGBITS section is detected.  Disable all warnings unless the (new) lint mode is enabled.

	* readelf.c (warn): New function - like elfcomm.c version but only
	produces output if warnings are enabled.
	(struct options): Add --lint and --enable-checks.
	(usage): Add entry for --lint.
	(parse_args): Handle -L.  If checks are enabled but no dumps have
	been selected then enable all dumps.
	(process_section_headers): Replace long if-then-else sequence with
	a switch.  Add warning messages for empty SHT_REL, SHT_RELA and
	SHT_PROGBITS sections.
	(process_file): Do not complain if the file is an archive and lint
	mode has been enabled.
	* elfcomm.c (error): Make the function weak.
	(warn): Likewise.
	* NEWS: Mention the new feature.
	* doc/binutils.texi: Document the new feature.
	* dwarf.h (report_leb_status): Add file name and line number
	parameters.  Include them in the diagnostic output.
	(READ_ULEB): Pass file and line number to report_leb_status.
	(READ_SLEB): Likewise.
	* dwarf.c (read_and_print_leb128): Pass file and line number to
	report_leb_status.
	* testsuite/binutils-all/readelf.exp: Add test of new feature.
	* testsuite/binutils-all/zero-sec.s: New test source file.
	* testsuite/binutils-all/zero-sec.r: Expected output from new
	test.