Add _datetime to the frozen modules.

I have no idea if this will fix the Windows build, but let's hope.

Author: ZeroIntensity

PCbuild/_freeze_module.vcxproj

@@ -106,6 +106,7 @@
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="..\Modules\atexitmodule.c" />
+    <ClCompile Include="..\Modules\_datetimemodule.c" />
     <ClCompile Include="..\Modules\faulthandler.c" />
     <ClCompile Include="..\Modules\gcmodule.c" />
     <ClCompile Include="..\Modules\getbuildinfo.c" />