targets: export radeon winsys_create functions to silence LLVM warning

It silences the following radeonsi LLVM warning due to a previous
commit adding an LLVM workaround:
  "mesa: for the -simplifycfg-sink-common option: may only occur zero or one
   times!"

Cc: 17.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by; Emil Velikov <emil.velikov@collabora.com>

(cherry picked from commit 18b12bf53351e1a902dc1f2e527a94ec8d8f3eff)
3 files changed