message: Set CMP0091 CMake policy
  This allows the correct use of runtime library override.
  Fixes
diff: @@ -44,6 +44,11 @@ option(PUGIXML_NO_STL "Disable STL" OFF)
  option(PUGIXML_NO_EXCEPTIONS "Disable Exceptions" OFF)
  mark_as_advanced(PUGIXML_NO_XPATH PUGIXML_NO_STL PUGIXML_NO_EXCEPTIONS)
  +# Policy configuration
  +if(POLICY CMP0091)
  + cmake_policy(SET CMP0091 NEW) # Enables use of MSVC_RUNTIME_LIBRARY
  +endif()
  +
  set(PUGIXML_PUBLIC_DEFINITIONS
  $<$<BOOL:${PUGIXML_WCHAR_MODE}>:PUGIXML_WCHAR_MODE>
  $<$<BOOL:${PUGIXML_COMPACT}>:PUGIXML_COMPACT>
  