Testing static and shared builds

[Zimmermann Paul]

>   for abi in `available-abis`; do
>     mkdir build-$abi-shared;
>     (cd build-$abi-shared \
>         && ../configure ABI=$abo --enable-shared \
>         && make && make check)
>     mkdir build-$abi-static;
>     (cd build-$abi-static \
>         && ../configure ABI=$abo --disable-shared \
>         && make && make check)
>   done

since this functionality might be useful for other projects (e.g., GNU MPFR),
maybe one should ask the autotools developers to provide it?

Paul