xfree86: #ifdef HAS_USL_VTS for switch_to under Solaris

switch_to() is only used from #ifdef HAS_USL_VTS code, place it inside
ifdefs to to avoid unused static warning and compile error on systems
without VT_ACTIVATE and VT_WAITACTIVE defines.

hw/xfree86/os-support/solaris/sun_init.c

@@ -61,6 +61,7 @@ static char consoleDev[PATH_MAX] = "/dev/fb";
    Used by hw/xfree86/common/xf86AutoConfig.c for VIS_GETIDENTIFIER */
 _X_HIDDEN char xf86SolarisFbDev[PATH_MAX] = "/dev/fb";
 
+#ifdef HAS_USL_VTS
 static void
 switch_to(int vt, const char *from)
 {
@@ -76,6 +77,7 @@ switch_to(int vt, const char *from)
         xf86Msg(X_WARNING, "%s: VT_WAITACTIVE failed: %s\n",
                 from, strerror(errno));
 }
+#endif
 
 void
 xf86OpenConsole(void)