compilation fix in cross_field_missmatch

Former-commit-id: 809f126237c4efa7560f8d6897420168a15fcfed

include/igl/cross_field_missmatch.cpp

@@ -8,7 +8,7 @@
 
 #include "cross_field_missmatch.h"
 
-
+#include <cmath>
 #include <vector>
 #include <deque>
 #include <igl/comb_cross_field.h>
@@ -64,7 +64,7 @@ namespace igl {
       //    std::cerr << "Dani: " << dir0(0) << " " << dir0(1) << " " << dir0(2) << " " << dir1Rot(0) << " " << dir1Rot(1) << " " << dir1Rot(2) << " " << angle_diff << std::endl;
 
       double step=M_PI/2.0;
-      int i=(int)floor((angle_diff/step)+0.5);
+      int i=(int)std::floor((angle_diff/step)+0.5);
       int k=0;
       if (i>=0)
         k=i%4;