Zstandard support for setup

[Jon Turney]

On 11/08/2018 20:52, Achim Gratz wrote:
[...]
> 
> The current code is available here:
> 
> http://repo.or.cz/w/cygwin-setup/local.git

Some comments:

This should check for ztd in configure.ac using PKG_CHECK_MODULES, 
rather than just assuming -lzstd is going to work.

The setup executables are cross-built on Fedora, so a 
mingw{32,64}-zstd-static package will need to become available.

compress_zstd.c:

+ using namespace std;

Please don't

compress_zstd.h:

+/* this is the parent class for all compress IO operations.
+ */

Comment is incorrect

I'd suggest removing all the 'virtual' since this class is final, but 
since all the compress subclasses have it, don't bother.

> The debug output statements are still in the code (although commented),
> I'll let that sit a while and see if I find something else I want to
> clean up before I submit it for the upstream repo.

I'd suggest keeping potentially useful ones under #ifdef DEBUG/#endif 
rather than just removing them all.