Correctly use abs(), fabs() and fabsf() where required. Silences clang warnings.

src/cell.c

@@ -793,7 +793,7 @@ int cell_are_neighbours(const struct cell *restrict ci,
   for (int k = 0; k < 3; k++) {
     const double center_i = ci->loc[k];
     const double center_j = cj->loc[k];
-    if (fabsf(center_i - center_j) > min_dist) return 0;
+    if (fabs(center_i - center_j) > min_dist) return 0;
   }
 
   return 1;
@@ -823,7 +823,7 @@ void cell_check_multipole(struct cell *c, void *data) {
             mb.mass);
 
     for (int k = 0; k < 3; ++k)
-      if (fabsf(ma.CoM[k] - mb.CoM[k]) / fabsf(ma.CoM[k] + mb.CoM[k]) > 1e-5)
+      if (fabs(ma.CoM[k] - mb.CoM[k]) / fabs(ma.CoM[k] + mb.CoM[k]) > 1e-5)
         error("Multipole CoM are different (%12.15e vs. %12.15e", ma.CoM[k],
               mb.CoM[k]);
 

src/debug.c

@@ -171,7 +171,7 @@ int checkSpacehmax(struct space *s) {
   }
 
   /*  If within some epsilon we are OK. */
-  if (abs(cell_h_max - part_h_max) <= FLT_EPSILON) return 1;
+  if (fabsf(cell_h_max - part_h_max) <= FLT_EPSILON) return 1;
 
   /* There is a problem. Hunt it down. */
   for (int k = 0; k < s->nr_cells; k++) {