Enables the use of SSE4.2 instructions on x86_64 CPUs, allowing
compilers to automatically vectorize some loops on citra_common.
A CMake toggle ENABLE_SSE42 (ON by default) has been added
to enable this behaviour.
This change breaks compatibility with CPUs that do not have
SSE4.2 instructions. All modern CPUs (from 2011 onwards) should
always have these instructions. Manual compilation will be
needed for older CPUs.
A message has been added to report if the CPU is incompatible
when starting the emulator.
Co-authored-by: OpenSauce04 <opensauce04@gmail.com>
