egl: Add Haiku code and support

* This is the cleaned up work of the Haiku GCI student
  Adrián Arroyo Calle adrian.arroyocalle@gmail.com
* Several patches were consolidated to prevent
  unnecessary touching of non-related code
diff --git a/src/SConscript b/src/SConscript
index 2657bba..eb4cd3c 100644
--- a/src/SConscript
+++ b/src/SConscript
@@ -33,6 +33,10 @@
     if env['platform'] not in ('cygwin', 'darwin', 'freebsd', 'haiku', 'windows'):
         SConscript('glx/SConscript')
     if env['platform'] not in ['darwin', 'haiku', 'sunos']:
+        SConscript('egl/drivers/dri2/SConscript')
+        SConscript('egl/main/SConscript')
+    if env['platform'] == 'haiku':
+        SConscript('egl/drivers/haiku/SConscript')
         SConscript('egl/main/SConscript')
 
     if env['gles']: