Use gen-libm-test.py to generate ulps table for manual

[Joseph Myers]

On Tue, 4 Sep 2018, Zack Weinberg wrote:

> The Debian equivalent, (lib)python2.7-minimal, has a README with an
> exact list of modules that may be used.  This appears to be a subset
> of the stuff in SUSE's python3-base  I've reproduced the contents of
> that file (from unstable; specifically, 2.7.15-3_amd64.deb) below.

That list does not include argparse.  I think we should be able to use 
argparse in the glibc build.

-- 
Joseph S. Myers
joseph@codesourcery.com