emulator/opengl: Get rid of all compiler warnings (Linux).

This patch gets rid of all compiler warnings for the
GPU emulation libraries when building on a Linux host.

Note that GLcommon/GLutils.h now provides two new functions
to perform 'safe' type casts between unsigned integers and
pointers: SafePointerFromUInt() and SafeUIntFromPointer().

Change-Id: I01c48bbd72f925d70eb9831f57e15815e687121f
15 files changed