Add pigz as gzip-native alternative.

Add pigz as gzip-native alternative.

pigz, which stands for parallel implementation of gzip, is a fully functional replacement for gzip that exploits multiple processors and multiple cores to the hilt when compressing data. pigz was written by Mark Adler, and uses the zlib and pthread libraries.

This recipe adds pigz as an alternative gzip-native implementation only.

Signed-off-by: Björn Stenberg <bjst@enea.com>