[CMake] 64bit format

[frederic heem]

Hi,
While trying to convert ethereal build system from autotool to cmake, I came 
across a problem which may be already solved.
There are three possible prefix for defining 64bit format: "%ll", "%L" 
and "%q". For instance, printing a signed decimal number could 
be "%lld", "%Ld" or "%qd".
If someone has already implemented these checks, I would be glad to use them. 
The last thing I want to do is to reinvent the wheel.
Thanks,
Frederic Heem