[CMake] Default CMAKE_C_FLAGS value by OS

[ycollette.nospam at free.fr]

Hello,

My question is related to CMAKE_*_FLAGS.
I've got a project under linux fedora 24 and, in release mode, this project compiles with the -O2 flag.
But when I switched to other platform (ubuntu, fedora 16 - I now this one is quite old but I need to compile on this platform), this default optimization flag changes. On some platform, it's -O3.
And because with -O3 flag some "risky" optimizations are enabled, my project hangs ...

Is it normal to have such a variations in default optimization flags in release mode ?

Best regards,

YC