[CMake] write file if different?

[Matthew Woehlke]

Is there a built-in way to write a string to a file (a la FILE(WRITE)) 
that will only write the file if the content would be different? (Or 
does FILE(WRITE) already work this way despite no obvious hint in the 
documentation that it does?)

Right now I am writing to a temporary file and running cmake -E 
copy_if_different, then removing the temporary file, but this seems 
inelegant and I am wondering if there is a better solution.

-- 
Matthew