allow using system icu in cross-compilation build

configure.in

@@ -1949,6 +1949,10 @@ AC_ARG_WITH(system-expat-for-build,
     AS_HELP_STRING([--with-system-expat-for-build],
         [Use expat/libxslt already on system for build tools (cross-compilation only).]))
 
+AC_ARG_WITH(system-icu-for-build,
+    AS_HELP_STRING([--with-system-icu-for-build],
+        [Use icu/libxslt already on system for build tools (cross-compilation only).]))
+
 AC_ARG_WITH(system-libxml-for-build,
     AS_HELP_STRING([--with-system-libxml-for-build],
         [Use libxml/libxslt already on system for build tools (cross-compilation only).]))
@@ -3191,6 +3195,7 @@ if test "$cross_compiling" = "yes"; then
     test -n "$with_system_cppunit_for_build" && sub_conf_opts="$sub_conf_opts --with-system-cppunit"
     test -n "$with_system_db_for_build" && sub_conf_opts="$sub_conf_opts --with-system-db"
     test -n "$with_system_expat_for_build" && sub_conf_opts="$sub_conf_opts --with-system-expat"
+    test -n "$with_system_icu_for_build" && sub_conf_opts="$sub_conf_opts --with-system-icu"
     test -n "$with_system_libxml_for_build" && sub_conf_opts="$sub_conf_opts --with-system-libxml"
     ./configure \
         --disable-mozilla \