cmake and RPATH

[Brad King]

Thiago Macieira wrote:
> Brad King wrote:
> 
>>Including an rpath pointing at the build tree has been a default in
>>CMake for many years.  All of Kitware's projects run both from the build
>>tree and from the install tree so it makes sense for us (and is great
>>for debugging).
> 
> I think installing a binary with the rpath pointing to the build-tree is a 
> no-no. That's just unclean.

Of course it is unclean, which is why I'm fixing it.  In the past we 
generally built with CMAKE_SKIP_RPATH enabled before installing.

> Also, take into account that linking takes a considerable amount of time 
> on a KDE build. I've just built kdebase on a 20-node compile farm. It 
> took 32 minutes: the last 10 of which were spent linking, without hitting 
> the compile farm at all. Installation took another 4 minutes.
> 
> That means 14 minutes that could be spent building 50% of the next module  
> in my build (kdepim). Imagine if I had been using cmake's 
> relink-when-installing feature: it would have been ~20 minutes * 19 
> machines of CPU time wasted, or a 42% increase in starvation.
> 
> So I think KDE needs a default which is to have rpath point to the 
> installation point but not the build-tree.

I'll make the feature available in CMake and KDE can use it if it wants.

-Brad