checks: Fix -Wunused-variable warnings

lib/gmath/la.c

@@ -215,7 +215,6 @@ mat_struct *G_matrix_scalar_mul(double scalar, mat_struct * matrix,
                                 mat_struct * out)
 {
     int m, n, i, j;
-    int index = 0;
 
     if (matrix == NULL) {
         G_warning(_("Input matrix is uninitialized"));
@@ -968,7 +967,7 @@ vec_struct *G_matvect_product(mat_struct * A, vec_struct * b,
 
     for (i = 0; i < m; i++) {
         sum = 0.0;
-        int width = A->rows;
+        /* int width = A->rows; */
 
         for (j = 0; j < n; j++) {
 
@@ -1602,7 +1601,7 @@ mat_struct *G_matrix_resize(mat_struct * in, int rows, int cols)
     mat_struct *matrix;
 
     matrix = G_matrix_init(rows, cols, rows);
-    int i, j, p, index = 0;
+    int i, j, p /*, index = 0 */ ;
 
     for (i = 0; i < rows; i++)
         for (j = 0; j < cols; j++)

lib/vector/Vlib/write_pg.c

@@ -75,10 +75,11 @@ static int set_constraint_to_deferrable(struct Format_info_pg *, const char *,
                                         const char *, const char *,
                                         const char *, const char *);
 static dbDriver *open_db(struct Format_info_pg *);
-#endif
 
 static struct line_pnts *Points;
 
+#endif
+
 /*!
    \brief Writes feature on level 1 (PostGIS interface)
 

raster/r.spread/collect_ori.c

@@ -54,7 +54,6 @@ void collect_ori(int start_fd, int start_is_time)
     extern CELL *cell;
     extern CELL *map_base, *map_x_out, *map_y_out, *map_visit;
     extern float *map_out;
-    extern char buf[];
     extern float neg, zero;
     extern int BARRIER;
     extern int nrows, ncols;

visualization/ximgview/main.c

@@ -111,7 +111,7 @@ static void draw(void)
             unsigned char b = *p++;
             unsigned char g = *p++;
             unsigned char r = *p++;
-            unsigned char a = *p++;
+            /* unsigned char a = */ (void)*p++;
             unsigned long c = find_color(r, g, b);
 
             XPutPixel(ximg, col, row, c);