package/pound: fix pcre2 detection

Without this fix configure finds the host version of pcre2-config:
checking for pcre2-config... /home/autobuild/autobuild/instance-3/output-1/host/bin/pcre2-config

Fixes:
http://autobuild.buildroot.net/results/1b9/1b98078a28b478018cf60bae35974cb4033e2af0/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/pound/pound.mk

@@ -18,6 +18,8 @@ POUND_CONF_OPTS = \
 
 ifeq ($(BR2_PACKAGE_PCRE2),y)
 POUND_CONF_OPTS += --enable-pcreposix=pcre2
+POUND_CONF_ENV += \
+	ac_cv_path_PCRE2_CONFIG=$(STAGING_DIR)/usr/bin/pcre2-config
 POUND_DEPENDENCIES += pcre2
 else ifeq ($(BR2_PACKAGE_PCRE),y)
 POUND_CONF_OPTS += --enable-pcreposix=pcre1