auto merge of #18672 : brandonson/rust/functional-update-walk, r=nikomatsakis

Fixes #18567. `Struct{x:foo, .. with_expr}` did not walk `with_expr`, which allowed
using moved variables in some cases.  The CFG for structs also built up with
`with_expr` happening before the fields, which is now reversed. (Fields are now
before the `with_expr` in the CFG)

diff --cc src/librustc/middle/cfg/construct.rs
Simple merge

diff --cc src/librustc/middle/expr_use_visitor.rs
Simple merge