Prevent install python-prctl outside Linux when installing by wheel (#1148). (#1151)
Prevent install python-prctl outside Linux when installing by wheel (#1148). (#1151)

When tensorpack was installed by wheel the platform was already evaluated
and thus python-prctl was installed, even though it is Linux-specific.
Installing from source package or sources was OK.

Instead use a platform specifier that is evaluated while installing the wheel.
ppwwyyxx/tensorpack,ppwwyyxx/tensorpack