The cmake config on the build system actually decides the release build optimization policy.
On Fedora, it's -O2. On Ubuntu, it's -O3.
Anything given in CMakeLists.txt is overridden by the build system policy since it goes at
the end of the compiler commandline.
When you are building cross, the build system's opinion of your cross binary optimization
level is irrelevant, and at worst destructive. Some versions of gcc contain broken optimizations
that are applied only at -O3.
This patch removes any doomed attempt to set -O in CMakeLists.txt, which has
no effect since the build system policy is still added at the end, but
removes confusion; and adds code to all the cross build files to forcibly
override release optimization level to -O2, removing the build system's
opinion of how your cross build should look.
