Bug#733770: linux-libc-dev: linux/btrfs.h: 'NULL' undeclared

["Aaron M. Ucko" <ucko@debian.org>]

Package: linux-libc-dev
Version: 3.11.10-1
Severity: important
Control: affects -1 src:trinity

Attempting to #include <linux/btrfs.h> without first ensuring a
definition of NULL (for instancy, by including <stddef.h>) fails:

  /usr/include/linux/btrfs.h: In function 'btrfs_err_str':
  /usr/include/linux/btrfs.h:511:11: error: 'NULL' undeclared (first use in this function)
      return NULL;
             ^
  /usr/include/linux/btrfs.h:511:11: note: each undeclared identifier is reported only once for each function it appears in

As a result, trinity FTBFS:

https://buildd.debian.org/status/fetch.php?pkg=trinity&arch=amd64&ver=1.2-1&stamp=1388344679

Could you please take a look?

Thanks!