This will make the *.entries files the the authoritative place to
define additional GL function prototypes. All generated header
files are now placed inside the build directory so that nobody
will ever try to touch them again.
This gets us rid of one unneeded socket based communication point which
we kept around for historic reasons (from Android QEMU) but don't really
need in our case. This allows a simplication of our setup and improves
performance.
