Work around a module build failure on the bots.

This patch works around what looks like a bug in Clang itself.

The error on the bot is:

https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/40466/consoleText

In module 'LLVM_Utils' imported from /Users/buildslave/jenkins/workspace/lldb-cmake/llvm-project/lldb/source/Plugins/ScriptInterpreter/Python/lldb-python.h:18:
/Users/buildslave/jenkins/workspace/lldb-cmake/llvm-project/llvm/include/llvm/Support/Error.h:720:3: error: 'llvm::Expected<bool>::(anonymous)' from module 'LLVM_Utils.Support.Error' is not present in definition of 'llvm::Expected<bool>' in module 'LLVM_Utils.Support.Error'
  union {
  ^
/Users/buildslave/jenkins/workspace/lldb-cmake/llvm-project/llvm/include/llvm/Support/Error.h:720:3: note: declaration of '' does not match
/Users/buildslave/jenkins/workspace/lldb-cmake/llvm-project/llvm/include/llvm/Support/Error.h:720:3: note: declaration of '' does not match
1 error generated.

The intention is to revert this as soon as a proper fix has been identified!

rdar://87845391