More fixes for PowerPC 64-bits

Still WIP.

I would need a review;

• https://lab.nexedi.com/nexedi/slapos/commit/f48accbeb9eccf622ef99ddacfd665634b13c6c0

First, updates openblas to 0.3.10 because PowerPC 64-bits has proper support there, is that a problem? Second, I removed the BINARY variable because I noticed it auto-detects from running system, is that OK?

• https://lab.nexedi.com/nexedi/slapos/commit/4b036c82444626806a7f48663c26a00ec4e5184e

I updated erp5's greenlet to 0.4.16 because it has proper PowerPC 64-bits support there, that should not have any greater impact, correct?

And for future reference, is there a way to make parts of a buildout configuration conditional for an architecture? I'm not speaking of shell commands but actual configuration.