Check the instruction set first in GPUinit, GPUconfigure and GPUtext
to prevent unsupported vector instructions from being executed.
Move the vector initialisation in GPUinit to a separate function - it
avoids a vzeroupper instruction.
vector push_back causes a SIGILL signal on a Nehalem (SSE4.2) QEMU VM
when compiled with GCC 6.1.1.
However, an empty constructor causes illegal instruction exceptions to be
generated on a Windows VM.
So here's an inbetween that looks stupid but works on what I've tested.
Jonathan Li