James Bottomley authored Jun 28, 2020 and Daiki Ueno committed Jun 29, 2020

On a very recent openSUSE build, libgnutls is getting built without
libpthread. This caused a thread related error when trying to load a
pkcs11 module that uses threading. The reason is rather convoluted:
glibc actually controls all the pthread_ function calls, but it
returns success without doing anything unless -lpthread is in the link
list. What's happening is that gnutls_system_mutex_init() is being
called on _gnutls_pkcs11_mutex before library pthreading is
initialized, so the pthread_mutex_init ends up being a nop. Then, when
the pkcs11 module is loaded, pthreads get initialized and the call to
pthread_mutex_lock is real, but errors out on the uninitialized mutex.

The problem seems to be that nothing in the gnulib macros gnutls
relies on for threading support detection actually sets LTLIBPTHREAD,
they only set LIBPTHREAD. The fix is to use LIBPTHREAD in
lib/Makefile.in

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>