Pull in _FORTIFY_SOURCE=3 stack smashing fix. Without the change on
current `master` `rtorrent` crashes at start as:
*** buffer overflow detected ***: terminated
__pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
44 pthread_kill.c: No such file or directory.
(gdb) bt
#0 __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
#1 0x00007ffff7880af3 in __pthread_kill_internal (signo=6, threadid=<optimized out>) at pthread_kill.c:78
#2 0x00007ffff7831c86 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#3 0x00007ffff781b8ba in __GI_abort () at abort.c:79
#4 0x00007ffff781c5f5 in __libc_message (fmt=fmt@entry=0x7ffff7992540 "*** %s ***: terminated\n") at ../sysdeps/posix/libc_fatal.c:150
#5 0x00007ffff7910679 in __GI___fortify_fail (msg=msg@entry=0x7ffff79924e6 "buffer overflow detected") at fortify_fail.c:24
#6 0x00007ffff790eea4 in __GI___chk_fail () at chk_fail.c:28
#7 0x00007ffff790ea85 in ___snprintf_chk (s=<optimized out>, maxlen=<optimized out>, flag=<optimized out>, slen=<optimized out>, format=<optimized out>) at snprintf_chk.c:29
#8 0x0000000000472acf in utils::Lockfile::try_lock() ()
#9 0x000000000044b524 in core::DownloadStore::enable(bool) ()
#10 0x00000000004b1f7b in Control::initialize() ()
#11 0x000000000043000b in main ()
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