[OE-core] Performance tweaks in 2.2

[Richard Purdie]

I've been distracted with ELC-E and other travel but I wanted to
recognise some good work people have done on the performance front. We
identified a few issues recently:

a) pseudo slowed down after upgrading sqlite
b) we were using more space on disk (without rm_work)
c) eSDK installation times had increased.

At the end of this email I've included some raw data from the
performance test scripts. The bottom line is that with the sqlite
regression fixed, we gained around 40s on builds and probably sped up
the SDK installation. Thanks to Jianxun Zhang for that! SDK install
times are down from 6 minutes to under 4 minutes, thanks Randy Witt.
Jussi Kukkonen also found a vala dependency issue which was bloating
the build footprint by ~200MB and makes another nice saving. Keeping an
eye on this does therefore make a difference and lots of small tweaks
do mount up.

We're still slightly slower than 2.1, mostly due to gcc6 being slower
and python3 but its better than it was and we at least have tracked
down some of the things we can fix.

Cheers,

Richard

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