meson: update llvm dependency logic for meson 0.54.0

meson: update llvm dependency logic for meson 0.54.0

In meson 0.54.0 I fixed the llvm cmake dependency to return "not found"
if shared linking is requested. This means that for 0.54.0 and later we
don't need to do anything, and for earlier versions we only need to
change the logic to force the config-tool method if shared linking is
required.

Fixes: 821cf6942a390f5f64d8a2cff9933b24c84f7dc1
       ("meson: Use cmake to find LLVM when building for window")

Acked-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4556>