cmake: Fix install of libclang-cpp.so when LLVM_INSTALL_TOOLCHAIN_ONLY=ON
cmake: Fix install of libclang-cpp.so when LLVM_INSTALL_TOOLCHAIN_ONLY=ON

Summary:
If CLANG_LINK_CLANG_DYLIB is also enabled, then this library needs to be
installed.

Fixes PR42575.

Reviewers: beanz, smeenai

Subscribers: mgorny, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64582

Conflicts:
	clang/tools/clang-shlib/CMakeLists.txt

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@365905 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang