Configure --without-sendmail (fixes #63891)

Pull request for [issue #63891](https://bugs.php.net/bug.php?id=63891)

Adds` --with[out]-sendmail` although `--with-sendmail` will still
exclude sendmail functionality silently if the executable is not
found in the path. This is to maintain backwards compatibility.

I personally feel we should make sendmail required unless
`--without-sendmail` is used, but making an optional dependency
mandatory with configuration defaults is not my decision to make.