uClibc: Patch string.h to check for __USE_XOPEN2K8

Several functions were marked as GNU extensions while they're included
in POSIX.1-2008.
opendingux: GCW0: inittab: Root login on ttyS0
Allow partial coreutils build
uclibc: fix an annoying warning
opendingux: GCW0: rcS: pass $INITFILE to the sourced scripts
Link /etc/shadow to /etc/local/shadow
opendingux: GCW0: Merge /etc/shadow on rootfs updates
oepndingux: GCW0: Enable shadow passwd in uclibc and busybox
opendingux: GCW0: Create /etc/local/shadow on boot if absent