Bug 1245076 - Include cmath instead of math.h in Collider.cpp. r=jfkthame

The combination of math.h being included and unified sources made abs()
in UtfCodec.h mean something different, failing the build with
libstdc++6 headers.

gfx/graphite2/src/Collider.cpp

@@ -26,7 +26,7 @@ of the License or (at your option) any later version.
 */
 #include <algorithm>
 #include <limits>
-#include <math.h>
+#include <cmath>
 #include <string>
 #include <functional>
 #include "inc/Collider.h"