Use VirtualAlloc() instead of mmap() on Windows

src/core/System.cc

@@ -1,9 +1,13 @@
 #include "System.h"
 #include <stdio.h>
 #include <unistd.h>
-#include <sys/mman.h>
 #include <stdint.h>
 #include <fcntl.h>
+#ifdef PLATFORM_WINDOWS
+#include "windows.h"
+#else
+#include <sys/mman.h>
+#endif
 
 unsigned long System::page_size;
 unsigned int System::page_size_log;
@@ -63,18 +67,30 @@ bool System::init(char * argv[])
 
 void * System::alloc_pages(int num)
 {
+#ifdef PLATFORM_WINDOWS
+    return VirtualAlloc(
+            NULL,
+            num << System::page_size_log,
+            MEM_COMMIT | MEM_RESERVE,
+            PAGE_READWRITE);
+#else
     return mmap(
             NULL,
-            num * System::page_size,
+            num << System::page_size_log,
             PROT_READ | PROT_WRITE,
             MAP_PRIVATE | MAP_ANONYMOUS,
             -1,
             0);
+#endif
 }
 
 void System::free_pages(void * addr, int num)
 {
+#ifdef PLATFORM_WINDOWS
+    (void)VirtualFree(addr, 0, MEM_RELEASE);
+#else
     (void)munmap(addr, num << System::page_size_log);
+#endif
 }
 
 std::string System::executable_path()