Added OSG_CPP_EXCEPTIONS_AVAILABLE cmake option to enable optional build of plugins and examples that required C++ exceptions

src/osgPlugins/png/ReaderWriterPNG.cpp

@@ -51,7 +51,11 @@ private:
 
 void user_error_fn(png_structp png_ptr, png_const_charp error_msg)
 {
+#ifdef OSG_CPP_EXCEPTIONS_AVAILABLE
     throw PNGError(error_msg);
+#else
+    osg::notify(osg::WARN) << "PNG lib warning : " << error_msg << std::endl;
+#endif
 }
 
 void user_warning_fn(png_structp png_ptr, png_const_charp warning_msg)
@@ -166,9 +170,10 @@ class ReaderWriterPNG : public osgDB::ReaderWriter
             // Set custom error handlers
             png_set_error_fn(png, png_get_error_ptr(png), user_error_fn, user_warning_fn);
 
+            #ifdef OSG_CPP_EXCEPTIONS_AVAILABLE
             try
+            #endif
             {
-
                 info = png_create_info_struct(png);
                 endinfo = png_create_info_struct(png);
 
@@ -300,13 +305,16 @@ class ReaderWriterPNG : public osgDB::ReaderWriter
                     osg::Image::USE_NEW_DELETE);
 
                 return pOsgImage;
+
             }
+            #ifdef OSG_CPP_EXCEPTIONS_AVAILABLE
             catch (PNGError& err)
             {
                 osg::notify(osg::WARN) << err << std::endl;
                 png_destroy_read_struct(&png, &info, &endinfo);
                 return ReadResult::ERROR_IN_READING_FILE;
             }
+            #endif
         }
 
         int getCompressionLevel(const osgDB::ReaderWriter::Options *options) const