Add {get,set}domainname(2)

{get,set}domainname aren't in POSIX but are widely-implemented
extensions.

The Linux kernel provides a setdomainname syscall but not a symmetric
getdomainname syscall, since it expects userspace to get the domain name
from uname(2).

Change-Id: I96726c242f4bb646c130b361688328b0b97269a0
Signed-off-by: Greg Hackmann <ghackmann@google.com>
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index d5dd206..b774dbc 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -327,6 +327,7 @@
 int setfsgid(gid_t)  all
 int setfsuid(uid_t)  all
 
+int setdomainname(const char*, size_t)  all
 int sethostname(const char*, size_t)  all
 
 pid_t wait4(pid_t, int*, int, struct rusage*)  all