Moves a few Cmake options so that debug options are near one another.
Moves GDBSTUB to the top as well where it should be.
Adds Link Time Optimization cmake option.

Adds a LTO option that isn't enabled by default.
Allows building release binaries with link time optimizations without generating a -dirty build.
Not enabled by default due to concerns of memory usage and increased build time.
Merge pull request #301 from Sonicadvance1/LTO-option

Adds Link Time Optimization cmake option.