add -march=i586 to lflags as well as cflags where appropriate
add -march=i586 to lflags as well as cflags where appropriate

When link time optimization is enabled, we need to remind the compiler
that we're targeting i586 when linking so it can resolve atomic
operations like __sync_bool_compare_and_swap.

bigfatbrowncat/avian-pack.avian,MaartenR/avian,ucdseniordesign/avian,getlantern/avian,ucdseniordesign/avian,bigfatbrowncat/avian-pack.avian,bigfatbrowncat/avian-pack.avian,bgould/avian,lwahlmeier/avian,bigfatbrowncat/avian-pack.avian,marcinolawski/avian,lwahlmeier/avian,MaartenR/avian,joshuawarner32/avian,bgould/avian,getlantern/avian,lostdj/avian,bgould/avian,minor-jason/avian,marcinolawski/avian,getlantern/avian,minor-jason/avian,lostdj/avian,ucdseniordesign/avian,dicej/avian,lostdj/avian,bgould/avian,dicej/avian,lwahlmeier/avian,dicej/avian,joshuawarner32/avian,lwahlmeier/avian,marcinolawski/avian,joshuawarner32/avian,getlantern/avian,joshuawarner32/avian,MaartenR/avian,marcinolawski/avian,ucdseniordesign/avian,minor-jason/avian,dicej/avian,lostdj/avian,minor-jason/avian,MaartenR/avian