Added code to fallback to Yosemite or pre-Yosemite system font in case current system font can't be found or is in an unusable format. San Francisco font used on current OS X versions is in a .otf file whih presumably means it has CFF outlines that stb_truetype can't use.

    dc.l $0, start
start:
	moveq #42, d0
	bsr fib
	reset
fib:
	cmp.l #2, d0
	blt base
	subq.l #1, d0
	move.l d0, -(a7)
	bsr fib
	move.l (a7), d1
	exg d0, d1
	move.l d1, (a7)
	subq.l #1, d0
	bsr fib
	move.l (a7)+, d1
	add.l d1, d0
	rts
base:
	moveq #1, d0
	rts