Remove lldb-private headers when building LLDB.framework with CMake

Summary:
Generating LLDB.framework when building with CMake+Ninja will copy the
lldb-private headers because public_headers contains them, even though we try
to make sure they don't get copied by removing root_private_headers from
root_public_headers.

This patch also removes SystemInitializerFull.h from the LLDB.framework headers when building with CMake.

Reviewers: compnerd, sas, labath, beanz, zturner

Reviewed By: labath

Subscribers: clayborg, mgorny, lldb-commits

Differential Revision: https://reviews.llvm.org/D47278

llvm-svn: 333444