[lldb][CMake] Disable modules in Xcode projects

Summary: Apparently, module-enabled builds clash with Xcode's analysis.

Reviewers: aprantl, jingham, davide, teemperor

Reviewed By: davide

Subscribers: mgorny, lldb-commits, #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D65874

llvm-svn: 368294