kconfig: fix gconfig with POSIXLY_CORRECT=1

This patch fixed "make gconfig" with POSIXLY_CORRECT=1 set.

This issue was reported by Jens Elkner <elkner@linofee.org> in kernel
Bugzilla #2919.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>