osx: fix c++11 build failure

* move from 'math.h' to 'cmath' header

Error:
smithdiagram.cpp:64:11: error: expected unqualified-id
  if(std::isfinite(*px))

qucs-transcalc/c_microstrip.cpp

@@ -29,7 +29,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
-#include <math.h>
+#include <cmath>
 
 #include "units.h"
 #include "transline.h"

qucs/diagrams/curvediagram.cpp

@@ -23,7 +23,7 @@
 #if HAVE_CONFIG_H
 # include <config.h>
 #endif
-#include <math.h>
+#include <cmath>
 #include <float.h>
 #if HAVE_IEEEFP_H
 # include <ieeefp.h>

qucs/diagrams/diagram.cpp

@@ -28,7 +28,7 @@
 # include <config.h>
 #endif
 #include <stdlib.h>
-#include <math.h>
+#include <cmath>
 #include <float.h>
 #if HAVE_IEEEFP_H
 # include <ieeefp.h>

qucs/diagrams/polardiagram.cpp

@@ -23,7 +23,7 @@
 #if HAVE_CONFIG_H
 # include <config.h>
 #endif
-#include <math.h>
+#include <cmath>
 #include <float.h>
 #if HAVE_IEEEFP_H
 # include <ieeefp.h>

qucs/diagrams/psdiagram.cpp

@@ -23,7 +23,7 @@
 #if HAVE_CONFIG_H
 # include <config.h>
 #endif
-#include <math.h>
+#include <cmath>
 #include <float.h>
 #if HAVE_IEEEFP_H
 # include <ieeefp.h>

qucs/diagrams/rect3ddiagram.cpp

@@ -26,7 +26,7 @@
 # include <config.h>
 #endif
 #include <stdlib.h>
-#include <math.h>
+#include <cmath>
 #include <float.h>
 #include <limits.h>
 #if HAVE_IEEEFP_H

qucs/diagrams/rectdiagram.cpp

@@ -25,7 +25,7 @@
 #if HAVE_CONFIG_H
 # include <config.h>
 #endif
-#include <math.h>
+#include <cmath>
 #include <float.h>
 #if HAVE_IEEEFP_H
 # include <ieeefp.h>

qucs/diagrams/smithdiagram.cpp

@@ -23,7 +23,7 @@
 #if HAVE_CONFIG_H
 # include <config.h>
 #endif
-#include <math.h>
+#include <cmath>
 #include <float.h>
 #if HAVE_IEEEFP_H
 # include <ieeefp.h>