It's needed for the next commit, as thanks to wxWidgets
anything using the precompiled header would default to 0x0600 (Vista)
instead of 0x0602 (Win8).
Now-redundant WINNT definitions resulting in macro redefinition
warnings have been removed.
Fix codegen on x86-64
Part 1 of the changes being worked on in #3451
Makes x86emitter emit the x86-64 machine code you would expect it to
Also adds some unit tests to verify that things are working