better CMake .gitignore [skip ci]

Author: scivision

cmake/options.cmake

@@ -21,7 +21,4 @@ if(CMAKE_PREFIX_PATH)
   get_filename_component(CMAKE_PREFIX_PATH ${CMAKE_PREFIX_PATH} ABSOLUTE)
 endif()
 
-# --- auto-ignore build directory
-if(NOT EXISTS ${PROJECT_BINARY_DIR}/.gitignore)
-  file(WRITE ${PROJECT_BINARY_DIR}/.gitignore "*")
-endif()
+file(GENERATE OUTPUT .gitignore CONTENT "*")