FTBFS when building against latest mesa (9.0 based)

At the same time this package was updated at Ubuntu, a new mesa was pushed at the archive. As a result, the builds that took more time to initialize itself, were built agains the latest mesa that was already available at the archive.

Build log: https://launchpadlibrarian.net/113429613/buildlog_ubuntu-quantal-armel.glmark2_2012.08-0ubuntu1_FAILEDTOBUILD.txt.gz

Relevant part:
[ 59/124] cxx: src/canvas-x11-glx.cpp -> build/src/canvas-x11-glx.cpp.2.o
../src/canvas-x11-glx.cpp: In member function 'virtual bool CanvasX11GLX::make_current()':
../src/canvas-x11-glx.cpp:63:69: error: invalid operands of types 'void' and 'int' to binary 'operator!='
Waf: Leaving directory `/build/buildd/glmark2-2012.08/build'
Build failed

That's because the function prototype got changed due version 33 of glxext.h:
-typedef int ( * PFNGLXSWAPINTERVALEXTPROC) (Display *dpy, GLXDrawable drawable, int interval);
+typedef void ( * PFNGLXSWAPINTERVALEXTPROC) (Display *dpy, GLXDrawable drawable, int interval);