gnutls: fix failure during do_compile

Add a Debian patch to fix a load of errors building the documentation
within do_compile e.g.:

| ./x509-api.texi:15: misplaced {
| ./x509-api.texi:15: misplaced }

(From OE-Core master rev: b09a9a5f298596795f17243e5ffcf7dab295a8e6)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>