Add guards for SPICE stuff

src/celengine/spiceinterface.cpp

@@ -9,6 +9,7 @@
 // as published by the Free Software Foundation; either version 2
 // of the License, or (at your option) any later version.
 
+#ifdef USE_SPICE
 #include "SpiceUsr.h"
 #include "spiceinterface.h"
 #include <cstdio>
@@ -113,3 +114,4 @@ bool LoadSpiceKernel(const string& filepath)
 		return true;
 	}
 }
+#endif

src/celengine/spiceorbit.cpp

@@ -9,6 +9,7 @@
 // as published by the Free Software Foundation; either version 2
 // of the License, or (at your option) any later version.
 
+#ifdef USE_SPICE
 #include <iostream>
 #include <cstdio>
 #include "SpiceUsr.h"
@@ -335,3 +336,4 @@ void SpiceOrbit::getValidRange(double& begin, double& end) const
     begin = validIntervalBegin;
     end = validIntervalEnd;
 }
+#endif

src/celengine/spicerotation.cpp

@@ -10,6 +10,7 @@
 // as published by the Free Software Foundation; either version 2
 // of the License, or (at your option) any later version.
 
+#ifdef USE_SPICE
 #include <iostream>
 #include <cstdio>
 #include <limits>
@@ -184,3 +185,4 @@ SpiceRotation::computeSpin(double jd) const
         return Quatd::yrotation(PI) * Quatd::xrotation(-PI / 2.0) * ~q * Quatd::xrotation(PI / 2.0);
     }
 }
+#endif