With glibc-2.16, using -D_FORTIFY_SOURCE requires that optimization (-O)
be used or it will prodice a warning message. Enable -Werror in our
test for _FORTIFY_SOURCE support to catch when a users specifies CFLAGS
without optimization.
The line to set CFLAGS="" when no CFLAGS are specified (either due to
being unset or geniunely empty) is required as autoconf will use
"-O2 -g" for its tests by defult when CFLAGS is unset, but will not add
them to the CFLAGS used...
Signed-off-by: Allan McRae <allan@archlinux.org>
d2669b4781