Linux: deploy libffi.so.6 (#2353).

CMakeLists.txt

@@ -1506,6 +1506,21 @@ else()
                 RENAME ${FULL_LIBRARY})
     endforeach()
 
+    # Library needed on Ubuntu 20.04 and later (while we build OpenCOR on Ubuntu
+    # 18.04 LTS)
+    # Note: the library is needed by Python, hence the user will need to
+    #       symbolically link this library to /usr/lib...
+
+    foreach(LIBRARY ffi.so.6)
+        set(FULL_LIBRARY ${CMAKE_SHARED_LIBRARY_PREFIX}${LIBRARY})
+
+        get_filename_component(REAL_FULL_LIBRARY /usr/lib/x86_64-linux-gnu/${FULL_LIBRARY} REALPATH)
+
+        install(FILES ${REAL_FULL_LIBRARY}
+                DESTINATION lib
+                RENAME ${FULL_LIBRARY})
+    endforeach()
+
     # Qt libraries required by OpenCOR
 
     foreach(QT_LIBRARY ${QT_LIBRARIES} DBus XcbQpa)