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/gallium/SConscript b/src/gallium/SConscript
index 977e3fb..25d0af6 100644
--- a/src/gallium/SConscript
+++ b/src/gallium/SConscript
@@ -63,7 +63,7 @@
 
 if not env['embedded']:
     SConscript('state_trackers/vega/SConscript')
-    if env['platform'] not in ('cygwin', 'darwin', 'freebsd', 'haiku', 'sunos'):
+    if env['platform'] not in ('cygwin', 'darwin', 'freebsd', 'sunos'):
         SConscript([
             'state_trackers/egl/SConscript',
             'targets/egl-static/SConscript',