AGG headers: remove use of deprecated register keyword, that is forbidden in C++17

Author: rouault

renderers/agg/include/agg_basics.h

@@ -211,7 +211,7 @@ namespace mapserver
     {
         AGG_INLINE static unsigned mul(unsigned a, unsigned b)
         {
-            register unsigned q = a * b + (1 << (Shift-1));
+            const unsigned q = a * b + (1 << (Shift-1));
             return (q + (q >> Shift)) >> Shift;
         }
     };

renderers/agg/include/agg_image_accessors.h

@@ -174,8 +174,8 @@ namespace mapserver
     private:
         AGG_INLINE const int8u* pixel() const
         {
-            register int x = m_x;
-            register int y = m_y;
+            int x = m_x;
+            int y = m_y;
             if(x < 0) x = 0;
             if(y < 0) y = 0;
             if(x >= (int)m_pixf->width())  x = m_pixf->width() - 1;

renderers/agg/include/agg_trans_affine.h

@@ -292,25 +292,25 @@ namespace mapserver
     //------------------------------------------------------------------------
     inline void trans_affine::transform(double* x, double* y) const
     {
-        register double tmp = *x;
+        const double tmp = *x;
         *x = tmp * sx  + *y * shx + tx;
         *y = tmp * shy + *y * sy  + ty;
     }
 
     //------------------------------------------------------------------------
     inline void trans_affine::transform_2x2(double* x, double* y) const
     {
-        register double tmp = *x;
+        const double tmp = *x;
         *x = tmp * sx  + *y * shx;
         *y = tmp * shy + *y * sy;
     }
 
     //------------------------------------------------------------------------
     inline void trans_affine::inverse_transform(double* x, double* y) const
     {
-        register double d = determinant_reciprocal();
-        register double a = (*x - tx) * d;
-        register double b = (*y - ty) * d;
+        const double d = determinant_reciprocal();
+        const double a = (*x - tx) * d;
+        const double b = (*y - ty) * d;
         *x = a * sy - b * shx;
         *y = b * sx - a * shy;
     }