[CMake] Preserve file date on copy

[Yann Renard]

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)

Anyone can help ?
Best regards,

Yann Renard