compiler: fix for expr sharing introduced by Order_eval::statement.

When processing an expression statement with a top-level call
that returns multiple results, Order_eval::statement can wind up
creating a tree that has multiple references to the same call,
which results in a confusing AST dump. Change the implementation
to avoid introducing this unwanted sharing.

Change-Id: I3781934a9358a3d3361c7baf24d305577c55cd29
Reviewed-on: https://go-review.googlesource.com/39210
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed