opengl: use compatibility profile

The GLSL shaders are written in GLSL 1.10 even though the OpenGL standard is
set to OpenGL ES 3.2 Core. Many platforms allow this but some platforms don't.
For standards compliance, it's probably a good idea in the future to upgrade
the shaders to 3.2, but for now we'll use 3.2 Compatibility which will allow the
GLSL 1.10 shaders to compile.

app/main.cpp

@@ -47,7 +47,7 @@ int main(int argc, char *argv[]) {
   QSurfaceFormat format;
   format.setVersion(3, 2);
   format.setDepthBufferSize(24);
-  format.setProfile(QSurfaceFormat::CoreProfile);
+  format.setProfile(QSurfaceFormat::CompatibilityProfile);
   QSurfaceFormat::setDefaultFormat(format);
 
   // Try to share OpenGL contexts