Enable enablewarnings() for MSC

[starkos]

What does this PR do?

Adds support for Premake's enablewarnings() call to MSC and Visual Studio. From the original pull request: "This pull request makes it so any warnings that are specifically enabled are set to level 1, which enables them as long as the user has the warning level at least level 1."

h/t @TrianglesPCT for the idea.

How does this PR change Premake's behavior?

Values set for enablewarnings() will now be applied to the MSC switches. This may cause a change in behavior if warnings had been previously enabled but ignored.

Anything else we should know?

No.

Did you check all the boxes?

• Focus on a single fix or feature; remove any unrelated formatting or code changes
• Add unit tests showing fix or feature works; all tests pass
• Mention any related issues (n/a)
• Follow our coding conventions
• Minimize the number of commits

You can now support Premake on our OpenCollective. Your contributions help us spend more time responding to requests like these!

[starkos]

Not sure why some CI builds see the branch and others don't?

[samsinsane]

This looks like you've got CI setup on your fork, but it's using this repos details instead of your fork? I'm guessing you would just need to disable the CI configuration in your repo?