package/syslog-ng: fix segfault on startup due to pthread_atfork

package/syslog-ng: fix segfault on startup due to pthread_atfork

syslog-ng may segfault at startup (during library initialization, before
reaching main) in newer toolchains. I have witnessed it on aarch64 (but with
32-bit arm userland) with glibc 2.28.

Problem is described in syslog-ng issue #2263 [1], which in turn leads to a
problem in 'ivykis' which is shipped with syslog-ng, see ivykis issue #15
[2].

Root cause is that 'pthread_atfork' is used by ivykis but searched by its
configure script in libpthread_nonshared only. In newer toolchains, it seems
this symbol is in libc_nonshared.

Apply a patch someone proposed via pullrequest [3] to the ivykis project,
but which is at this moment not yet merged upstream.

[1] https://github.com/balabit/syslog-ng/issues/2263
[2] https://github.com/buytenh/ivykis/issues/15
[3] https://github.com/buytenh/ivykis/pull/16

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>