Get fork() working on Windows

This is done without using Microsoft's internal APIs. MAP_PRIVATE
mappings are copied to the subprocess via a pipe, since Microsoft
doesn't want us to have proper COW pages. MAP_SHARED mappings are
remapped without needing to do any copying. Global variables need
copying along with the stack and the whole heap of anonymous mem.
This actually improves the reliability of the redbean http server
although one shouldn't expect 10k+ connections on a home computer
that isn't running software built to serve like Linux or FreeBSD.

libc/isystem/windows.h

@@ -69,9 +69,9 @@
 #define PINT_PTR       intptr_t*
 #define UINT_PTR       uintptr_t
 #define PUINT_PTR      uintptr_t*
-#define LONG_PTR       int32_t*
+#define LONG_PTR       intptr_t
 #define PLONG_PTR      int32_t**
-#define ULONG_PTR      uint32_t*
+#define ULONG_PTR      uintptr_t
 #define PULONG_PTR     uint32_t**
 #define POINTER_64_INT int64_t*
 #define __int3264      int64_t