Kconfig: Improve error messages for mismatched endchoice/endif/endmenu

Update Kconfiglib (and menuconfig, just to sync) to upstream revision
8087311cd91be to get the following fix in, for an issue reported by
pfalcon:

    Give clearer errors for bad endchoice/endif/endmenu nesting

    An endchoice/endif/endmenu with no corresponding choice/if/menu
    generated a cryptic 'unrecognized construct' parse error. Improve
    the error message so that the problem is pointed out explicitly:

      kconfiglib.KconfigError: Kconfig:37: couldn't parse 'endmenu': no
      corresponding 'menu'

    Reported in https://github.com/ulfalizer/Kconfiglib/issues/56

.

This update also adds support for user-defined preprocessor functions in
Python, which could potentially be handy for DTS/Kconfig integration.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>