Added stub for dbghelp.SymRegisterCallback64.
diff --git a/include/dbghelp.h b/include/dbghelp.h
index d5849a4..1d3c8a6 100644
--- a/include/dbghelp.h
+++ b/include/dbghelp.h
@@ -736,6 +736,8 @@
 BOOL WINAPI SymEnumerateSymbols(HANDLE, DWORD, PSYM_ENUMSYMBOLS_CALLBACK, PVOID);
 typedef BOOL (CALLBACK *PSYMBOL_REGISTERED_CALLBACK)(HANDLE, ULONG, PVOID, PVOID);
 BOOL WINAPI SymRegisterCallback(HANDLE, PSYMBOL_REGISTERED_CALLBACK, PVOID);
+typedef BOOL (CALLBACK *PSYMBOL_REGISTERED_CALLBACK64)(HANDLE, ULONG, ULONG64, ULONG64);
+BOOL WINAPI SymRegisterCallback64(HANDLE, PSYMBOL_REGISTERED_CALLBACK64, ULONG64);
 BOOL WINAPI SymUnDName(PIMAGEHLP_SYMBOL, PSTR, DWORD);
 DWORD WINAPI UnDecorateSymbolName(LPCSTR, LPSTR, DWORD, DWORD);