[cmake] Add all subprojects to LLVM_ALL_PROJECTS Make LLVM_ALL_PROJECTS reflect all top-level directories in the monorepo rather than an arbitrary subset. clang-tools-extra is technically unnecessary since it gets enabled by clang, but having it there for consistency shouldn't hurt either. Differential Revision: https://reviews.llvm.org/D57843 llvm-svn: 353346 GitOrigin-RevId: 351314a14f70246f1e873fe5bc04cbd70cbd6d92