gettext: fix static build failure

When static libraries are preferred we don't build dynamic libraries so
it fails on the install phase. So don't try to do it for those cases.
Fixes:
http://autobuild.buildroot.net/results/651537ae1909b039e0cfc5c104ee87f93a9e5792/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/gettext/gettext.mk

@@ -35,9 +35,12 @@ endif
 # When the gettext tools are not enabled in the configuration, we only
 # install libintl to the target.
 ifeq ($(BR2_PACKAGE_GETTEXT_TOOLS),)
+# When static libs are preferred the .so files aren't created
+ifeq ($(BR2_PREFER_STATIC_LIB),)
 define GETTEXT_INSTALL_TARGET_CMDS
 	cp -dpf $(STAGING_DIR)/usr/lib/libintl*.so* $(TARGET_DIR)/usr/lib/
 endef
+endif
 # Ditch the tools since they're off and pull other dependencies
 define GETTEXT_DISABLE_TOOLS
 	$(SED) 's/runtime gettext-tools/runtime/' $(@D)/Makefile.in