Implement POSIX lockf.

This has been requested a few times over the years. This is basically
a very late rebase of https://android-review.googlesource.com/45470
which was abandoned years ago. One addition is that this version has
_FILE_OFFSET_BITS=64 support.

POSIX puts this in <unistd.h>. glibc also has it in <fcntl.h>.

Bug: http://b/13077650
Change-Id: I5862b1dc326e326c01ad92438ecc1578d19ba739
diff --git a/libc/include/signal.h b/libc/include/signal.h
index 7a171b4..85c46c0 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -30,9 +30,9 @@
 #define _SIGNAL_H_
 
 #include <asm/sigcontext.h>
+#include <bits/pthread_types.h>
+#include <bits/timespec.h>
 #include <limits.h>
-#include <machine/pthread_types.h>
-#include <machine/timespec.h>
 #include <sys/cdefs.h>
 #include <sys/types.h>