Promote -B and -H from internal to experimental options
This pair makes it easier to avoid cluttering scripts or terminal sessions with cd
.
Using them alone (only -H or only -B) is confusing may issue warning.
There may also be longer variants like --source-directory=...
and --build-directory=...
.
Related link: http://public.kitware.com/pipermail/cmake-developers/2016-June/028843.html