[CMake] Accept ENTITLEMENTS in add_llvm_executable and llvm_codesign

Summary: Allow code-signing with entitlements. FORCE may be used to avoid an error when replacing existing signatures.

Reviewers: beanz, bogner

Reviewed By: beanz

Subscribers: mgorny, llvm-commits, lldb-commits

Differential Revision: https://reviews.llvm.org/D54443

llvm-svn: 347068