[CompilerRT] Attempt to fix a lit-config issue

This is a follow-up to 31125785 -- it looks like passing the added
cmake flag to pythonize_bool also appends "_PYBOOL" to the flag name, which
this lit config file is missing. This trips up builds such as:

  https://lab.llvm.org/buildbot/#/builders/275/builds/3661
  https://lab.llvm.org/buildbot/#/builders/184/builds/9811

Where COMPILER_RT_HAS_AARCH64_SME ends up expanding to nothing.