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/Emulator.h

@@ -37,6 +37,8 @@ namespace UserspaceEmulator {
 
 class Emulator {
 public:
+    static Emulator& the();
+
     Emulator(const Vector<String>& arguments, NonnullRefPtr<ELF::Loader>);
 
     bool load_elf();