GLES3 spec is worthless and only returns a boolean result for occlusion queries. This is fine for simple cellular games but we need more than a
boolean result.
Thankfully Nvidia exposes GL_NV_occlusion_queries under a OpenGL ES extension, which allows us to get full samples rendered.
The only device this change affects is the Nexus 9, since it is an Nvidia K1 crippled to only support OpenGL ES.
No other OpenGL ES device that I know of supports this extension.
This is good hygiene, and also happens to be required to build Dolphin
using Clang modules.
(Under this setup, each header file becomes a module, and each #include
is automatically translated to a module import. Recursive includes
still leak through (by default), but modules are compiled independently,
and can't depend on defines or types having previously been set up. The
main reason to retrofit it onto Dolphin is compilation performance - no
more textual includes whatsoever, rather than putting a few blessed
common headers into a PCH. Unfortunately, I found multiple Clang bugs
while trying to build Dolphin this way, so it's not ready yet, but I can
start with this prerequisite.)
