Allow defining multiple GCC O Levels [2/2]

Available GCC Optimization Levels
        -Os
        -O2 (Default)
        -O3

PS2: Commit msg...

Change-Id: I567e42ca0931006c9b81fce01d3ac7ecf421f508
Signed-off-by: Lokesh Chamane <lokesh.c703@gmail.com>