[CMake] avoid object file recompilation

[gga]

Timur Ivanov wrote:
> 
> The problem is that common.cpp recompiled 3 times but I would like not
> to do that waste of time. Is it possible ?

No and Yes.  No, cmake in general does not allow to do it easily or
reliably.

But your OS does.  Make common.cpp into either a static or dynamic
library and add it to your subprojects.  That's why you are using a make
system in the first place.

-- 
Gonzalo Garramuño
ggarra at advancedsl.com.ar

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