Implement _FILE_OFFSET_BITS (mostly).

I still don't think we can make stdio's fseeko and ftello work, but we can
have everything else, and very few programs use fseeko/ftello (and they can
just refrain from using _FILE_OFFSET_BITS and be no worse off than they are
today).

Bug: 11865851
Change-Id: Ic3cb409aae6713f4b345de954bcc4241fcd969ec
diff --git a/libc/include/sys/sendfile.h b/libc/include/sys/sendfile.h
index 81a3c44..c588e68 100644
--- a/libc/include/sys/sendfile.h
+++ b/libc/include/sys/sendfile.h
@@ -34,7 +34,11 @@
 
 __BEGIN_DECLS
 
+#if defined(__USE_FILE_OFFSET64)
+extern ssize_t sendfile(int out_fd, int in_fd, off_t* offset, size_t count) __RENAME(sendfile64);
+#else
 extern ssize_t sendfile(int out_fd, int in_fd, off_t* offset, size_t count);
+#endif
 extern ssize_t sendfile64(int out_fd, int in_fd, off64_t* offset, size_t count);
 
 __END_DECLS