Fix incorrect arch selection

Correct arch is 'x86', not 'x86_64'.  Who'd've thunk?
Clean up warning building python-rtai pkg
Fix build problem with compressed files

Compressing the ipipe patches in the `binary-indep` section when the
`rtai-source` package is a `binary-arch` package led to a race
condition where `dh_md5sum` failed to process a `.patch` file that had
been converted to `.patch.gz` without its knowledge.