[Cogl] WebOS support

[Neil Roberts]

Here are two patches to add basic support for using the WebOS version
of SDL.

WebOS has a specially patched version of SDL to add a mechanism for
creating a GLES context instead of a GL context. The API is actually
completely general and not tied to WebOS so presumably it could be
pushed into a real version of SDL. However it looks like development
on SDL 1.2 (which we are using) has stopped and SDL 1.3 already has a
different mechanism to request a GLES context. SDL 1.3 is unreleased
and will be API incompatible.

One caveat if anyone tries to build this is that SDL on WebOS
internally uses glib and runs the main loop in a secret extra thread
using the default context. I guess an application built for WebOS
shouldn't depend on the system providing glib because it's not part of
the API so when building it I made it use a statically linked version
of glib. However the libpdl.so provided with the SDK seems to try to
link to some glib symbols so if you're not careful the GCC linker will
automatically export the symbols from the static glib library that PDL
uses. To stop it doing this I made a stub version of libpdl.so which
has empty definitions of all the symbols and then passed
-Wl,--exclude-libs,libglib-2.0.a to the linker.