[CMake] CPack: Use an external tar program

[Jonathan Perkin]

Hi,

AIUI, cpack's tar support is done natively using libarchive.  I'd like
to instead use an external tar binary, in this case one which uses
pigz as the gzip backend, as it is massively faster on the hardware I
am building on.

Is there some trick I've not found to allow this, or is it
unsupported?

Thanks,

-- 
Jonathan Perkin, Release Engineering Manager, MySQL
Oracle Corporation UK Ltd.   http://oss.oracle.com/