rollup merge of #20425: sanxiyn/opt-local-ty

This avoids having ast::Ty nodes which have no counterpart in the source.

diff --cc src/librustc_trans/save/mod.rs
Simple merge

diff --cc src/librustc_typeck/check/mod.rs
Simple merge

diff --cc src/libsyntax/ast.rs
Simple merge

diff --cc src/libsyntax/parse/parser.rs
Simple merge