[flang] Fix CMake bug in the definition of flang-new

Recent patch that improved Flang's compatibility with respect to how LLVM
dynamic libraries should be linked (and specified in CMake recipes),
introduced a bug in the definition of `flang-new`:
  * https://reviews.llvm.org/D87893
More specifically, `add_flang_tool` does not support the
`LINK_COMPONENTS` CMake argument.  Instead, one should set
`LLVM_LINK_COMPONENTS` before calling `add_flang_tool`.

This patch reverts the change for `flang-new` from
https://reviews.llvm.org/D87893, and instead:
  * sets `LLVM_LINK_COMPONENTS`
  * calls `clang_target_link_libraries` to add Clang dependencies

Differential Revision: https://reviews.llvm.org/D89403