Make sure to link in libm.

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -267,7 +267,7 @@ include_directories(${CMAKE_SOURCE_DIR})
 if(NOT WIN32)
   # Create and install shared library on non-windows
   add_library(pano13 SHARED ${pano13_hdr} ${pano13_res} ${pano13_src})
-  target_link_libraries(pano13 ${_common_libs})
+  target_link_libraries(pano13 m ${_common_libs})
   set_target_properties(pano13 PROPERTIES VERSION "3.0.0" SOVERSION "3")
   install(TARGETS pano13 LIBRARY DESTINATION ${MYLIB} COMPONENT libraries)
   set(_pano_target pano13)