Some more trivial warning fixes

simgear/math/SGBox.hxx

@@ -97,7 +97,7 @@ public:
     return (_max[0] - _min[0])*(_max[1] - _min[1])*(_max[2] - _min[2]);
   }
 
-  const bool empty() const
+  bool empty() const
   { return !valid(); }
 
   bool valid() const

simgear/math/sg_random.h

@@ -40,7 +40,7 @@ extern "C" {
  * Structure to hold MT algorithm state to easily allow independant
  * sets of random numbers with different seeds.
  */
-struct {unsigned int array[MT_N]; int index; } typedef mt;
+typedef struct {unsigned int array[MT_N]; int index; } mt;
 
 /**
  * Initialize a new MT state with a given seed.