[Sema] Fix pointer-to-int-cast for MSVC build bot

Revision 9658d895 breaks the clang-x64-windows-msvc build bot [1].
This should fix the unit test using the same method as used in 9658d895.

Note I don't have access to a Windows system so the patch is based on the
errors generated by the bot.

[1] http://lab.llvm.org:8011/builders/clang-x64-windows-msvc/builds/14358

Differential Revision: https://reviews.llvm.org/D74694