[CMake] Preserve file date on copy

[Yann Renard]

Bill Hoffman wrote:
> Yann Renard wrote:
>> I have several modules managed with cmake and a script to build all 
>> the modules at once. When a simple module gets modified, cmake 
>> rebuilds what is needed in it and copies the API files in the include 
>> path. Those API files' date get modified at this time, resulting on 
>> the rebuild off all modules depending on this first simple module. My 
>> wish would be to avoid date change at copy time to free some time 
>> during build process. (copies are made thanks to cmake command mode 
>> calls)
> The best thing to do would be a copy if different.   If the files really 
> do change, then you would want a rebuild.  Both configure file and -E 
> copy_if_different will work.
> 
> -Bill

It seems it does what I need, thank you Bill !

Yann Renard