* fix(Makefile): Don't double up on optimisation flags
This is already provided by BUILD_CFLAGS later on
* feat(common): Mark explicitly-placed things as used
If we put something in a given section, we should be able to expect it to actually turn up in that section!
Doing this will prevent LTO from slurping all the hooks away as "unused".
* feat: Enable LTO
This uses "fat" binaries, so normal builds won't break, but also includes the LTO data for builds that wish to use it
