wgl: Add a stw_dev getter

Data imports need to be marked __declspec(dllimport), so
just export a function instead of data.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>
Reviewed By: Bill Kristiansen <billkris@microsoft.com>

Acked-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12727>

src/gallium/frontends/wgl/stw_device.c

@@ -186,6 +186,12 @@ stw_init_screen(HDC hdc)
    return stw_dev->screen != NULL;
 }
 
+struct stw_device *
+stw_get_device(void)
+{
+   return stw_dev;
+}
+
 boolean
 stw_init_thread(void)
 {

src/gallium/frontends/wgl/stw_device.h

@@ -99,6 +99,9 @@ extern struct stw_device *stw_dev;
 boolean
 stw_init_screen(HDC hdc);
 
+struct stw_device *
+stw_get_device(void);
+
 static inline struct stw_context *
 stw_lookup_context_locked( DHGLRC dhglrc )
 {