Add SHF_COMPRESSED support to readelf

Add SHF_COMPRESSED support to readelf

This patch updates readelf to dump compression header with

readelf -S -W:

  [ 4] .debug_info PROGBITS  00000000 000038 00007d 00   C 0   0  1

readelf -t -W:

  [ 4] .debug_info
       PROGBITS        00000000 000038 00007d 00   0   0  1
       [00000800]: COMPRESSED
       ZLIB, 0000009d, 1

It also checks the compression header when decompressing the compressed
section.

	* readelf.c (get_elf_section_flags): Support SHF_COMPRESSED.
	(get_compression_header): New.
	(process_section_headers): Dump compression header if needed.
	(uncompress_section_contents): Don't free compressed_buffer here.
	(load_specific_debug_section): Free the compressed buffer, update
	the section buffer and the section size if uncompress is
	successful.