Add missing file to glxtrace.so

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c731a36..6f22249 100755 (executable)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -294,6 +294,7 @@ else ()
         glsnapshot.cpp
         trace_writer.cpp
         image.cpp
+        image_png.cpp
         os_posix.cpp
     )