compiler plugin

[Norbert Thiebaud]

so I ran some number... after upgrading ccache

clang+pluging+dbgutil  (time result in minutes.. elapsed/user/system)

cold: 33/840/50
hot: 9/79/14
no-op: 4/46/1

clang+dbgutil (no plugins)

cold: 26/605/46
hot: 9/79/14
no-op: 4/46/1

gcc-dbgutil

cold: 28/621/97
hot: 9/79/14
no-op: 4/45/1

note: none of these comprise make check

so the cost of the plugins on a full build is 7 minutes elapsed, ~240
minutes cpu.

ccache works fine... on the other hand any change in any of the
plugins invalidate the cache...

I've enabled an additional build for gerrit doing clang + plugins on linux
we will see how that perform in average.
preliminary observation is that there is way to much churn in the
plugins for this to be viable at this time....

Norbert