Cmake 3 16

[milyin]

Fixed issues preventing build with cmake 3.16. The fixes are:

• use generator expressions only if multiconfig generator used (visual studio usually). On single config generators the generator expessions (like $<IF) doesn't appear anymore. This allows to avoid issues with insufficient genexpr support in old cmake
• variable CMAKE_CURRENT_FUNCTION_LIST_FILE not supported in cmake 3.16, the reloading of "helpers.cmake" changed to not use this variable