[clang] [clang][CMake] Fix clangSupport_tablegen ODR violation with LLVM_LINK_LLVM_DYLIB (PR #186672)

[Alexis Engelke via cfe-commits]

aengelke wrote:

The source files in clang/lib/Support should be compiled only once. These object files should get linked into libclang/clang (which link against libLLVM.so) and into clang-tblgen (which doesn't link against libLLVM.so). clang-tblgen shouldn't be linking against libLLVM.so, regardless of whether object libraries are used.

https://github.com/llvm/llvm-project/pull/186672