compiler: tweaks for importing inline function bodies

compiler: tweaks for importing inline function bodies

    Track whether we've seen an error when importing a function; we will
    use error tracking to avoid knock-on errors.

    Stop importing identifiers at a ')'.

    Provide a way to adjust the indentation level while importing.

    Reviewed-on: https://go-review.googlesource.com/c/150072

From-SVN: r266536