package/poppler: use THREAD_PTHREAD_ARG=OFF

As noted by Fabrice, all other packages that show CMake's FindThreads
issue fix it by setting THREAD_PTHREAD_ARG=OFF instead of setting
THREAD_HAVE_PTHREAD_ARG=ON. So, for consistency, do the same for
poppler.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/poppler/poppler.mk

@@ -21,7 +21,7 @@ POPPLER_CONF_OPTS = \
 	-DENABLE_GTK_DOC=OFF
 
 # cmake older than 3.10 requires this to avoid try_run() in FindThreads
-POPPLER_CONF_OPTS += -DTHREADS_HAVE_PTHREAD_ARG=ON
+POPPLER_CONF_OPTS += -DTHREADS_PTHREAD_ARG=OFF
 
 ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
 POPPLER_CONF_OPTS += -DCMAKE_CXX_FLAGS="$(TARGET_CXXFLAGS) -latomic"