make: disable makeinfo exec due to texinfo 5.x compat issue

Newer texinfo versions lose compatibility with make.texi, and lacking
expertise with texinfo, we'll disable makeinfo use, otherwise we can get build
failures.

Signed-off-by: Christopher Larson <kergoth@gmail.com>
Merge pull request #70 from kergoth/sb-1766

make: disable makeinfo exec due to texinfo 5.x compat issue