RFC: Add support for SHF_COMPRESSED

[Cary Coutant]

> I added --compressed-debug-sections=[none|zlib] to as and
> objcopy.  I updated gold to decompress SHF_COMPRESSED
> section.  I didn't add --compressed-debug-sections=[none|zlib]
> to gold since I don't know if this name is a final choice nor
> gold maintainers want such an option.

objcopy, gas, and gold already have the --compress-debug-sections
option (though only gold takes "=[none|zlib]" as a parameter; objcopy
and gas always use zlib, and spell the negative as
--nocompress-debug-sections).

I don't see any point in adding another option, especially one spelled
so similarly -- just use the existing option and make it generate the
new form, after all the consumers understand both formats. (And I
prefer a verb to an adjective.)

If you want the option to generate either format, how about something
like "--compress-debug-sections=[none|zlib|zlib-old|zlib-new]"? (Where
"zlib" would generate the old for a while, then we'd switch it to the
new after some time.

-cary