Changed nmake to build against MSVCRT (/MD, /MDd)

[gh-andre]

• When the runtime type option is omitted, VC++ builds object files with a LIBCMT directive, which is a thread-safe CRT statically linked runtime library.
• This change adds explicit release and debug dynamic CRT options into build configurations.

[pablodelara]

Thanks for this PR, @gh-andre. Could you sign off the commit as per the contributing guidelines? Thanks!

[gh-andre]

I don't have GPG setup to sign commits and these 2 lines are not worth the trouble. Just apply the patch from the issue, if you want to fix Windows builds.

[pablodelara]

Hi @gh-andre. Actually, it doesn't involve any GPG. All you would need to do is use "git commit -s" to add the "Signed-off-by" line, with your name and email. Agree that I can just take the code and apply it, but I want you to get the credit. Thanks for your work.

[gh-andre]

Thanks for your kind words. I'm pretty sure it requires some setup for this command to work, but I will give it a try this weekend and will let you know.

[gh-andre]

@pablodelara I clearly misunderstood the --signoff option in that it only made sense in my mind if this sign-off was cryptographically signed. My bad.

I added the sign-off trailer in a new pull request. Have a look, and if I messed up anything else, please feel free to reject the pull request and just grab the patch.