[CMake] How do I set generated scripts executable in CMakeLists.txt?

[kent williams]

Say I generate a script using CONFIGURE_FILE.  How would I make it
executable?  In other words, is there a CMake way of doing this that
will work on all CMake platforms?

The way we deal with portability in our particular case is to use Tcl
scripts.  Our stuff won't work on any platform without tcl, so tclsh
is the 'most portable' script processor.