message: Fix up doc to reflect latest semantics change
diff: @@ -517,16 +517,11 @@ that are _always_ built for the host platform.
  allows users to opt into different (and more consistent) behavior for
  these properties.
  -When `target-applies-to-host` is unset in the configuration file, the
  -existing Cargo behavior is preserved (though see `-Zhost-config`, which
  -changes that default). When it is set to `true`, _all_ options from
  -`[target.<host triple>]` are respected for host artifacts. When it is
  -set to `false`, _no_ options from `[target.<host triple>]` are respected
  -for host artifacts.
  -
  -In the specific case of `rustflags`, this settings also affects whether
  -`--target <host-triple>` picks up the same configuration as if
  -`--target` was not supplied in the first place.
  +When `target-applies-to-host` is unset, or set to `true`, in the
  +configuration file, the existing Cargo behavior is preserved (though see
  +`-Zhost-config`, which changes that default). When it is set to `false`,
  +no options from `[target.<host triple>]` are respected for host
  +artifacts.
  In the future, `target-applies-to-host` may end up defaulting to `false`
  to provide more sane and consistent default behavior. When set to
  