Makefile: Add LTO Optimization

Link Time Optimization (LTO) gives GCC the capability of dumping its internal representation (GIMPLE) to disk, so that all the different compilation units that make up a single executable can be optimized as a single module. This expands the scope of inter-procedural optimizations to encompass the whole program (or, rather, everything that is visible at link time). More about LTO can be found here https://gcc.gnu.org/wiki/LinkTimeOptimization
Thanks @Cl3Kener

Signed-off-by: Lens-F <tnoah12@gmail.com>

Conflicts:
	Makefile

Conflicts:
	Makefile