UserspaceEmulator: Make mmap'ed memory track read/write protection

Here's the first time we get a taste of better information than the
real hardware can give us: unlike x86 CPUs, we can actually support
write-only memory, so now we do!

While this isn't immediately useful, it's still pretty cool. :^)

DevTools/UserspaceEmulator/CMakeLists.txt

@@ -1,5 +1,6 @@
 set(SOURCES
     Emulator.cpp
+    MmapRegion.cpp
     SimpleRegion.cpp
     SoftCPU.cpp
     SoftMMU.cpp