Resolve "--optimize compiler option does not work for ARM-based CPUs"

@bkarlsen @schwarz

My dear colleagues, currently I have no ARM environment to play a bit with the compiler options, so I'll leave it up to you.. This might be useful: https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html

I have included the fix from markus already in the branch.

Closes #54 (closed)