Glob patterns should be in POSIX style, so let's make sure that globs
like `../` are handled correctly.

If the incoming absolute path is already absolute, then we don't need to
try and resolve it again.

In v3 you can configure `content` to be relative to the
`tailwind.config.js` file instead of relative to the current working
directory of the process.

This ensures that the base is set correctly to the correct base instead.

No need to normalize the static part because it should already be in
POSIX style.