title: Multiplatform C++ cross-compiler
body: <p>How can I build a cross-compiler for a C++ library to target many platforms on a single build server?</p>
  
  <p>The cross-compiler should be able to build the library for (at least) {Windows 7, Mac OS X, Ubuntu 11.04} × {32 bit, 64 bit} × {Debug, Release}. I don't care if the whole build from scratch takes forever or if the <code>gcc</code> binary is 1 GB. If the cross-compiler cannot be a single executable, what is the workflow I should use to compile (and recompile) my library?</p>
  
  <p>The host machine would be a Ubuntu 11.04.</p>