Use decltype(sizeof(void*)) as a facsimile for std::size_t.

Clang demands that the size argument to the various operator new()'s
to be exactly whatever it thinks std::size_t is.

Since we can't include STL headers, this little trick will do.

AK/Types.h

@@ -11,7 +11,7 @@ typedef signed short signed_word;
 typedef signed int signed_dword;
 typedef signed long long int signed_qword;
 
-typedef unsigned long size_t;
+typedef decltype(sizeof(void*)) size_t;
 typedef long ssize_t;
 
 static_assert(sizeof(size_t) == sizeof(dword));