[libFuzzer] Add missing FuzzerBuiltinsMsvc.h include.

Should fix the Windows build.

GitOrigin-RevId: 1032886a41c6ef386e5280344958dbdba337779f
diff --git a/mutagen/MutagenDispatcher.cpp b/mutagen/MutagenDispatcher.cpp
index 4d3fa2b..32b5694 100644
--- a/mutagen/MutagenDispatcher.cpp
+++ b/mutagen/MutagenDispatcher.cpp
@@ -10,6 +10,7 @@
 
 #include "MutagenDispatcher.h"
 #include "FuzzerBuiltins.h"
+#include "FuzzerBuiltinsMsvc.h"
 #include "FuzzerPlatform.h"
 #include "MutagenUtil.h"
 #include <iomanip>