haiku: Fix build through scons corrections and viewport fixes

* Add HAVE_PTHREAD, we do have pthread support wrappers now for
  non-native Haiku threaded applications.
* Viewport changed behavior recently breaking the build.
  We fix this by looking at the gl_context ViewportArray
  (Thanks Brian for the idea)

Acked-by: Brian Paul <brianp@vmware.com>
2 files changed