compiler: Accept map composite literals with omitted key types.

compiler: Accept map composite literals with omitted key types.

    compiler: Copy key_path_ when copying a Composite_literal_expression.

    Fixes golang/go#10263.

    Reviewed-on: https://go-review.googlesource.com/14299
    Reviewed-on: https://go-review.googlesource.com/18988

From-SVN: r232892