From Alberto Luaces, "the new changes in osgAnimation showed some errors on the Cygwin

platform:

1 - osgAnimation/StatsHandler includes <cmath>, but on Cygwin only std::isnan
is defined that way. I changed it to <math.h> as it is done in the rest of
the OSG.

2 - Pulling some osgViewer headers from the same file in osgAnimation makes
the former a new dependency. Thus, I got errors at osgAnimation linking time.
I wonder why nobody noticed this on other platforms. I have updated the
CMakeLists.txt file in order to link to the needed libraries, and

3 - I have updated the openscenegraph-osgAnimation.pc.in file accordingly."

src/osgAnimation/StatsHandler.cpp

@@ -14,7 +14,7 @@
 #include <sstream>
 #include <iomanip>
 #include <stdio.h>
-#include <cmath>
+#include <math.h>
 
 #include <osg/io_utils>
 #include <osg/NodeVisitor>