[ThinLTO] Force disable test on Windows via REQUIRES shell

The "XFAIL: win32" was not enough to get the test to XFAIL on the bot:
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast/builds/5478

For now, use "REQUIRES: shell" to suppress test on Windows while we
investigate.

llvm-svn: 269777