36411219 had preprocessor issues on Windows.
This should now work on all platforms.

I had to change UNIMPLEMENTED() and UNREACHABLE() to always take a
format parameter to make this work on MSVC. This doesn't seem like
a terrible thing though - especially if we can incorporate the
frequency of hit UNIMPLEMENTED()'s to steer our focus.

Change-Id: Idc58dbe6caa3fb51e085c3b236904c640091deec
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27468
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>