gettext-full: avoid using iconv for host builds

The gettext-full host build might pick up iconv-stub host build  headers
during the build, leading to stray linker errors with unresolved references
to libiconv_open(), libiconv() and libiconv_close().

Since we're not needing iconv support on the host, pass the appropriate
cache variables to configure to prevent detection and linking of iconv.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/libs/gettext-full/Makefile

@@ -71,7 +71,10 @@ HOST_CONFIGURE_ARGS += \
 
 
 HOST_CONFIGURE_VARS += \
-	EMACS="no"
+	EMACS="no" \
+	am_cv_lib_iconv=no \
+	am_cv_func_iconv=no \
+	ac_cv_header_iconv_h=no \
 
 define Build/InstallDev
 	$(INSTALL_DIR) $(1)/usr/lib/libintl-full/include