Consider inlining functions if the binary is smaller or the same size afterwards

[dylanmckay]

Posted by @ameisen in the avr-rust Gitter:

Something that avr-llvm should probably do automatically, but I have to use -finline-limit=10000000 for in gcc it should always inline a function if the binary is smaller or the same size afterwards.

there's no cache effects or such to worry about gcc is not smart enough to do it, I've noticed. -finline-limit=10000000 gives me smaller binaries.