[PATCH for-4.15] tools/configure: add bison as mandatory

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Roger Pau Monne writes ("[PATCH for-4.15] tools/configure: add bison as 
mandatory"):
> Bison is now mandatory when the pvshim build is enabled in order to
> generate the Kconfig.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Please re-run autogen.sh after applying.
> 
> Fallout from this patch can lead to broken configure script being
> generated or bison not detected correctly, but those will be cached
> quite quickly by the automated testing.

Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
Reviewed-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>

I've read the rest of the thread and I prefer Roger's version of this
patch.

Thanks,
Ian.