midori: add missing BR2_TOOLCHAIN_USES_GLIBC dependency

midori selects webkitgtk, and webkitgtk needs a glibc toolchain, but
midori did not propagate this dependency, causing the following kconfig
warning:

warning: (BR2_PACKAGE_MIDORI) selects BR2_PACKAGE_WEBKITGTK which has unmet direct dependencies (BR2_INSTALL_LIBSTDCPP && BR2_TOOLCHAIN_GCC_AT_LEAST_4_9 && BR2_TOOLCHAIN_USES_GLIBC && BR2_PACKAGE_LIBGTK3 && BR2_PACKAGE_WEBKITGTK_ARCH_SUPPORTS)

Interestingly, the Config.in comment of the midori package already
mentionned the (e)glibc dependency, but the BR2_TOOLCHAIN_USES_GLIBC
dependency was not expressed (either on the comment or on the main
package option itself).

Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>