Explicitly link poppler-glib against pthread

Debian complains about missing symbols:

dpkg-shlibdeps: warning: symbol pthread_mutexattr_destroy used by debian/libpoppler-glib8/usr/lib/i386-linux-gnu/libpoppler-glib.so.8.6.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol pthread_mutexattr_init used by debian/libpoppler-glib8/usr/lib/i386-linux-gnu/libpoppler-glib.so.8.6.0 found in none of the libraries
dpkg-shlibdeps: warning: symbol pthread_mutexattr_settype used by debian/libpoppler-glib8/usr/lib/i386-linux-gnu/libpoppler-glib.so.8.6.0 found in none of the libraries

https://bugs.freedesktop.org/show_bug.cgi?id=91450
1 file changed