Index: VTK-9.0.0/ThirdParty/libharu/vtklibharu/CMakeLists.txt
===================================================================
--- VTK-9.0.0.orig/ThirdParty/libharu/vtklibharu/CMakeLists.txt
+++ VTK-9.0.0/ThirdParty/libharu/vtklibharu/CMakeLists.txt
@@ -125,6 +125,8 @@ if(PNG_FOUND)
 endif(PNG_FOUND)
 endif ()
 
+link_libraries(m)
+
 # =======================================================================
 # configure header files, add compiler flags
 # =======================================================================