[Development] QtWebEngine on x86 without SSE2

[Kevin Kofler]

PS:
> I verified that this builds on GNU/Linux on i686, on x86_64 (where SSE2 is
> part of the baseline and can thus be assumed safely) and on ARM (where
> SSE2 does not exist at all and so the patch should have no effect). I have
> not done runtime testing yet.

I have now done a basic functionality test in QEMU-KVM, both with the 
default SSE2-enabled qemu64 CPU and with "-cpu pentium3" (which claims to 
not support SSE2 in cpuid), and in both cases things appear to work. I am 
not aware of any testing done on a real non-SSE2 machine though. (The KVM 
test with the fake cpuid tests that the non-SSE2 code paths don't crash, but 
it does not guarantee that there are really no SSE2 instructions 
encountered. That can only be reliably verified with full software CPU 
emulation or with a real non-SSE2 CPU.)

        Kevin Kofler