libqrencode: link with pthread to avoid build failure

Fixes: http://autobuild.buildroot.net/results/1ca0719dd1fe0bbc528ec99b5bc2b42e985bfdca/

[Peter: only if toolchain has threads, pass --disable-thread-safety otherwise]
Signed-off-by: Danomi Manchego <danomimanchego123@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libqrencode/libqrencode.mk

@@ -11,6 +11,12 @@ LIBQRENCODE_INSTALL_STAGING = YES
 LIBQRENCODE_LICENSE = LGPLv2.1+
 LIBQRENCODE_LICENSE_FILES = COPYING
 
+ifeq ($(BR2_TOOLCHAIN_HAS_THREADS),y)
+LIBQRENCODE_CONF_ENV += LIBS='-pthread'
+else
+LIBQRENCODE_CONF_OPT += --disable-thread-safety
+endif
+
 ifeq ($(BR2_PACKAGE_LIBQRENCODE_TOOLS),y)
 LIBQRENCODE_CONF_OPT += --with-tools=yes
 LIBQRENCODE_DEPENDENCIES += libpng