libpayload: Add qsort()

It's taken from OpenBSD and thus appropriately licensed (and reasonably
tested).

Change-Id: I5767600c9865d39e56c220b52e045f3501875b98
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/88
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

payloads/libpayload/libc/Makefile.inc

@@ -34,6 +34,7 @@ libc-$(CONFIG_LIBC) += rand.c time.c exec.c
 libc-$(CONFIG_LIBC) += readline.c getopt_long.c sysinfo.c
 libc-$(CONFIG_LIBC) += args.c strings.c
 libc-$(CONFIG_LIBC) += strlcpy.c
+libc-$(CONFIG_LIBC) += qsort.c
 
 # should be moved to coreboot directory
 libc-$(CONFIG_LAR) += lar.c