Add extended attribute (xattr) system call wrappers to bionic.

The xattr system calls are required for the SE Android userspace in
order to get and set file security contexts.  In particular, libselinux
requires these calls.

Change-Id: I78f5eb3d8f3384aed0a5e7c6a6f001781d982017
diff --git a/libc/include/sys/linux-unistd.h b/libc/include/sys/linux-unistd.h
index f060374..693302d 100644
--- a/libc/include/sys/linux-unistd.h
+++ b/libc/include/sys/linux-unistd.h
@@ -98,6 +98,10 @@
 int              fchownat (int dirfd, const char *path, uid_t owner, gid_t group, int flags);
 int              fchmodat (int dirfd, const char *path, mode_t mode, int flags);
 int              renameat (int olddirfd, const char *oldpath, int newdirfd, const char *newpath);
+int              fsetxattr (int, const char *, const void *, size_t, int);
+ssize_t          fgetxattr (int, const char *, void *, size_t);
+ssize_t          flistxattr (int, char *, size_t);
+int              fremovexattr (int, const char *);
 int              link (const char*, const char*);
 int              unlink (const char*);
 int              unlinkat (int, const char *, int);
@@ -121,6 +125,14 @@
 int              symlink (const char *, const char *);
 int              fchdir (int);
 int              truncate (const char*, off_t);
+int              setxattr (const char *, const char *, const void *, size_t, int);
+int              lsetxattr (const char *, const char *, const void *, size_t, int);
+ssize_t          getxattr (const char *, const char *, void *, size_t);
+ssize_t          lgetxattr (const char *, const char *, void *, size_t);
+ssize_t          listxattr (const char *, char *, size_t);
+ssize_t          llistxattr (const char *, char *, size_t);
+int              removexattr (const char *, const char *);
+int              lremovexattr (const char *, const char *);
 int              __statfs64 (const char *, size_t, struct statfs *);
 int              pause (void);
 int              gettimeofday (struct timeval*, struct timezone*);