Mark optimized modulo and memcpy code pages -w after writing them.

src/platform.h

Index: src/platform.h
===================================================================
--- src/platform.h	(revision 8772)
+++ src/platform.h	(working copy)
@@ -207,6 +207,9 @@
                         bool is_executable);
   static void Free(void* address, const size_t size);
 
+  // Mark code segments non-writable.
+  static void ProtectCode(void* address, const size_t size);
+
   // Assign memory as a guard page so that access will cause an exception.
   static void Guard(void* address, const size_t size);