flex: fix configure cache issue with BR2_NEEDS_GETTEXT

Flex doesn't NEED gettext/libintl, but it's configure script checks for it,
so make sure those a built before flex, otherwise flex will populate
tgt-config.cache with invalid values, breaking the build of other packages
needing it (like libglib2).

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/flex/flex.mk

@@ -10,6 +10,9 @@ FLEX_PATCH:=flex_$(FLEX_VERSION)-$(FLEX_PATCH_VERSION).diff.gz
 FLEX_SITE:=$(BR2_DEBIAN_MIRROR)/debian/pool/main/f/flex
 FLEX_DIR:=$(BUILD_DIR)/flex-$(FLEX_VERSION)
 FLEX_INSTALL_STAGING=YES
+FLEX_DEPENDENCIES = \
+	$(if $(BR2_PACKAGE_GETTEXT),gettext) \
+	$(if $(BR2_PACKAGE_LIBINTL),libintl)
 
 # lex -> flex
 define FLEX_INSTALL_LEX