cmake: Enable -fwrapv by default.
cmake: Enable -fwrapv by default.

The code base contains code that assumes a great deal of behavior about
how integers behave on overflow.  I've tried to find and eliminated
these but in case I haven't, we can at least get the compiler to help.

ShiftMediaProject/game-music-emu,ShiftMediaProject/game-music-emu,ShiftMediaProject/game-music-emu