binutils: fix build with host gcc < 4.9

binutils 2.27 checks if the target compiler supports -Wstack-
usage=262144, and also uses this setting for the host compiler. If the
host compiler is gcc < 4.9 binutils build will fail. This backports 2
commits which are fixing this problem for binutils 2.28.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>