Add builds with \MD flag for building Python extensions

[tkralphs]

No description provided.

[jhmgoossens]

See comment on PR #673 regarding MSVC MT and MD artifacts, notably MT missing libgcc_s_seh.

[jhmgoossens]

@tkralphs I propose to Close this PR and I will make PRs for all stables of all projects to use --enable-msvc=MD so the binaries are really MD and not MT binaries called "-md" as is the case currently.

Details:
This PR 674 build for stable:

• The MSVC MT binaries (~14.7MB zip) are NOT working due to missing libgcc_s_seh-1.dll and libstdc++-6.dll
• The MSVC MD binaries (~17.7MB zip) are working and no reference to libgcc_s_seh and libstdc++-6., but no CoinUtils-0.dll etc. Only one large executable for Clp.exe and Cbc.exe. And these binaries really are "MD" because they indeed dynamically link to MS C runtime libraries.

The current stable build has binaries called "-md", but (as you noticed) those are really MT binaries. This is caused by the fact that we simplified the windows-ci.yml in stable to --enable-msvc (like in master), but we (I) didn't realize that the configure in master and stable are actually different in this respect: master configure expects --enable-msvc while stable configure supports --enable-msvc=MD, though "=MT" doesnt work (see above). Conclusion: In stable to make MD binaries use --enable-msvc=MD and to make MT binaries use --enable-msvc. Maybe stable configure can be fixed here, but master configure already has this fixed by only supporting --enable-msvc which makes proper MD binaries.

Since the aim of this PR is to make MD binaries for stable (not to make also good MT binaries) I propose to close this PR.
Instead, I will make PRs for all stables because they all currently produce binaries that work (phew) but that are called "-md" but are in fact all "MT". The easiest way in stable to make good MD binaries is simply to replace --enable-msvc with --enable-msvc=MD. Let me know if you disagree.

Again, thanks to Stefan.

[tkralphs]

Yes, I agree, the cleanest thing to do is to fix all the projects, although I think it is really only a big issue for Cbc itself.