package/pure-ftpd: fix static build with openssl and latomic

Use pkg-config to find openssl dependencies such as lz or latomic

Fixes:
 - http://autobuild.buildroot.org/results/eba8d344446b0db6327c0588c456c14594984f76

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit ff5504b4daea7e3979980a61b62dcd3c68f0eb30)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/pure-ftpd/pure-ftpd.mk

@@ -40,10 +40,8 @@ endif
 
 ifeq ($(BR2_PACKAGE_OPENSSL),y)
 PURE_FTPD_CONF_OPTS += --with-tls
-PURE_FTPD_DEPENDENCIES += openssl
-ifeq ($(BR2_STATIC_LIBS),y)
-PURE_FTPD_CONF_ENV += LIBS='-lssl -lcrypto -lz'
-endif
+PURE_FTPD_DEPENDENCIES += host-pkgconf openssl
+PURE_FTPD_CONF_ENV += LIBS=`$(PKG_CONFIG_HOST_BINARY) --libs openssl`
 else
 PURE_FTPD_CONF_OPTS += --without-tls
 endif