Change default build to O2

[JackNewman12]

This works for me and it makes the UI feel a little snappier (could be placebo, not sure if the UI is firmware or screen hardware limited).

If I have a large number of local changes or custom images I find the firmware won't fit in memory with O3. I've made it O2 for now to save any future headaches from new features.

[Xenoamor]

That's interesting. The optimisation level is currently set here. I wonder if this is taking precedence over it It would be great to use O3, hopefully they get round to fixing the flto bug

[JackNewman12]

Good catch. Can't believe I didn't check that makefile. The -O2 I added gets appended after -Os in libopencm3.rules.mk

From the GCC manpage:

If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.

I will move my changes when I get home.

[Xenoamor]

If you move them then dpsboot will be compiled with it as well. It might make more sense where it currently is

[kanflo]

As soon as you move your changes @JackNewman12 I will merge this.

[Xenoamor]

We'll want to keep the bootloader as -Os I think. Give us the most FLASH we can for the application. The application as -O3 makes sense though if we can afford it