compiler: lvalue context fixes in Unary_expression::do_get_backend

A couple of the Backend::var_expression invocations in
Unary_expression::do_get_backend were selecting "lvalue" context
incorrectly (these var exprs were not in an assignment or LHS
position); fix is to change back to "rvalue" context.

Change-Id: I429cc214febfd6955f12384c0c515385059fb69c
Reviewed-on: https://go-review.googlesource.com/45136
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed