mini-gmp request for version inclusion

[Simon Sobisch]

Am 17.04.2020 um 10:21 schrieb paul zimmermann:
>        Dear Simon,
> 
>> We can already test for use of mini-gmp via __MINI_GMP_H__ (defined by
>> both mini-gmp.h and mini-gmp.c) but there's no version number available.
> 
> this issue was already reported in 2017:
> 
> https://gmplib.org/list-archives/gmp-devel/2017-December/004682.html
> 
> Best regards,
> Paul
> 

Thank you for the mention, of this thread (my impression from the
documention was that this belongs to the users' list, but the dev-list
may be more reasonable [and in any case I don't find a way to search in
either of them]).

So the status is:
* it was reported end of 2017
* there *is* a way to recognize mini-gmp now (which does not seem the
case back then) via __MINI_GMP_H__
* there is still no option (I've found) to recognize its version

Reasons for me to include it [together with a macro gmp_version]:

* remove the explicit need to check for __MINI_GMP_H__ to not call
gmp_version (for example in the programs --info option)
* easy way to tell (for example in configure) if the user puts in his
old mini-gmp which may be known to be bad for any reason

Simon