meson: Only draw with llvm depends on native directly

meson: Only draw with llvm depends on native directly
Tests, softpipe or AMD drivers don't depend on it directly

Fixes: 3955dd07 ("meson/gallium: Add an option to not use LLVM for gallium draw module")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/6817

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Tested-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Reviewed-by: Yonggang Luo <luoyonggang@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17675>