[clangd] Use clang_target_link_libraries() for clang libs (#94937)

Use clang_target_link_libraries() instead of LINK_LIBS when linking
clang libraries. This ensures that in CLANG_LINK_CLANG_DYLIB mode we
link against libclang-cpp.so (instead of linking against both it and the
static libraries).

Most places were already doing this correctly, there were just a handful
of leftovers.