[gentoo-devhelp] Building project twice in the same ebuild

[Nikos Chantziaras]

I need to build a project (which uses cmake) twice and install it twice. 
Each time with a different configuration. The files it generates in each 
configuration do not conflict with each other (except for share/doc/).

Which configs are built depends on USE flags. Either qt4, qt5 or both.

How would I go on about this? The project's build system *can not* build 
both sets in the same build. When building normally, outside of portage, 
this is built with:

   mkdir build && cd build
   cmake -DQT_VERSION=4 ../
   make && make install
   rm -r *
   cmake -DQT_VERSION=5 ../
   make && make install

I'm not sure I can do something like that in an ebuild.