package/dovecot: Add optional support for icu

Optional dependency added to fts plugin since Dovecot 2.2.17:
http://hg.dovecot.org/dovecot-2.2/diff/b179bbd226e5/configure.ac

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/dovecot/dovecot.mk

@@ -40,6 +40,13 @@ else
 DOVECOT_CONF_OPTS += --without-bzlib
 endif
 
+ifeq ($(BR2_PACKAGE_ICU),y)
+DOVECOT_CONF_OPTS += --with-icu
+DOVECOT_DEPENDENCIES += icu
+else
+DOVECOT_CONF_OPTS += --without-icu
+endif
+
 ifeq ($(BR2_PACKAGE_LIBCAP),y)
 DOVECOT_CONF_OPTS += --with-libcap
 DOVECOT_DEPENDENCIES += libcap