Generate version file to ensure proper version check

Signed-off-by: Kimball Thurston <kdt3rd@gmail.com>

IlmBase/config/CMakeLists.txt

@@ -101,7 +101,17 @@ endif()
 # The main export of the configuration - This is the
 # moral equivalent of a pkg-config file for cmake
 # and replaces the Find*.cmake of the "old" cmake
+include(CMakePackageConfigHelpers)
+write_basic_package_version_file("${PROJECT_NAME}ConfigVersion.cmake"
+  VERSION ${ILMBASE_VERSION}
+  COMPATIBILITY SameMajorVersion
+)
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake
+  DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}
+)
 install(EXPORT ${PROJECT_NAME}
   DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}
+  FILE ${PROJECT_NAME}Config.cmake
   NAMESPACE ${PROJECT_NAME}::
+  EXPORT_LINK_INTERFACE_LIBRARIES
 )