gl: Use core GL_STENCIL8_DEPTH24 for gl_flavor=desktop

Jesse complained that --enable-gl --enable-glesv2 wasn't pulling in the
right headers, and in particular GL_STENCIL8_DEPTH24_OES was undefined
but being used. In this case we can simply use the identical
GL_STENCIL8_DEPTH24 instead.

Reported-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/cairo-gl-device.c

@@ -319,7 +319,7 @@ _get_depth_stencil_format (cairo_gl_context_t *ctx)
 
 #if CAIRO_HAS_GLESV2_SURFACE
     if (ctx->gl_flavor == CAIRO_GL_FLAVOR_DESKTOP)
-	return GL_DEPTH24_STENCIL8_OES;
+	return GL_DEPTH24_STENCIL8;
 #endif
 
 #if CAIRO_HAS_GL_SURFACE