Source: http://git.videolan.org/?p=vlc/vlc-3.0.git;a=blob_plain;f=contrib/src/upnp/libpthread.patch
libupnp: -lpthread must be checked first

On GNU/Linux, -pthread does not work properly when linking a static
library that depends on POSIX threads. -lpthread must be checked first.

diff -Nru upnp.orig/m4/acx_pthread.m4 upnp/m4/acx_pthread.m4
--- upnp.orig/m4/acx_pthread.m4	2016-08-06 11:54:20.990800226 +0300
+++ upnp/m4/acx_pthread.m4	2016-08-06 11:54:37.909800395 +0300
@@ -123,7 +123,7 @@
 # which indicates that we try without any flags at all, and "pthread-config"
 # which is a program returning the flags for the Pth emulation library.
 
-acx_pthread_flags="pthreads none -Kthread -kthread lthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"
+acx_pthread_flags="pthreads none -Kthread -kthread lthread -lpthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"
 
 # The ordering *is* (sometimes) important.  Some notes on the
 # individual items follow: