Fix unused-var warnings from Clang.

simgear/environment/precipitation.hxx

@@ -42,7 +42,6 @@ private:
     float _rain_intensity;
     float _clip_distance;
 	
-    int _wind_dir;
     osg::Vec3 _wind_vec;
 	
     osg::ref_ptr<osgParticle::PrecipitationEffect> _precipitationEffect;

simgear/scene/sky/sky.hxx

@@ -237,7 +237,6 @@ private:
     float minimum_sky_visibility;
 
     int in_cloud;
-    int cur_layer_pos;
 
     // near cloud visibility state variables
     bool in_puff;

simgear/timing/sg_time.cxx

@@ -151,7 +151,6 @@ static double sidereal_course( time_t cur_time, const struct tm *gmt, double lng
 {
     time_t start_gmt, now;
     double diff, part, days, hours, lstTmp;
-    char tbuf[64];
   
     now = cur_time;
     start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);