Remove preprocessor hacks to choose JIT implementation.

Opens up for having multiple JIT implementations available at runtime,
which could be use for experimenting with new JIT compiler types or for
unit testing one JIT on another architecture.

Very few of the newly virtual calls are on any sort of critical path so
hopefully there will not be a performance loss.

Core/MemMap.cpp

@@ -35,6 +35,7 @@
 #include "Core/Debugger/Breakpoints.h"
 #include "Core/Config.h"
 #include "Core/HLE/ReplaceTables.h"
+#include "Core/MIPS/JitCommon/JitBlockCache.h"
 
 namespace Memory {