linux-user: fix getcwd syscall

linux-user: fix getcwd syscall

The patch called "prefer glibc over direct syscalls" (commit 7118) has
replaced the getcwd syscall with a call to the glibc. With this change,
the syscall is returning -1 in error case and 0 otherwise.
This is problematic as the sys_getcwd syscall should return the number
of bytes written to the buffer including the '\0'.

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Acked-By: Riku Voipio <riku.voipio@iki.fi>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@7130 c046a42c-6fe2-441c-8c8c-71466251a162