Added run_flags directive to `compiletest`

Now it is possible to specify run-flags in tests. For example, by using `run-flags: --bench` the Bencher is run.
shootout-threadring rewrite

* simplify the code
* remove trace to satisfy official shootout test
* use libgreen to improve performances
auto merge of #13553 : aochagavia/rust/pr, r=alexcrichton

Now it is possible to specify run-flags in tests. For example, by using `run-flags: --bench` the Bencher is run.
auto merge of #13656 : TeXitoi/rust/shootout-threadring-rewrite, r=alexcrichton

* simplify the code
* remove trace to satisfy official shootout test
* use libgreen to improve performances
rustc: move the method and vtable maps into ty::ctxt.
rustc: de-@ method and vtable maps.
rustc: de-@ ty::AutoAdjustment.
rustc: remove unused errors_reported field from regionck.
rustc: make MemCategorizationContext immutable.
rustc: de-@ lang_items.
rustc: de-@ some RefCell's.
rustc: de-@ freevars.
rustc: de-@ lint.
rustc: de-@ resolve.
rustc: de-@ borrowck.
rustc: de-@ mem_categorization.
rustc: de-@ metadata::cstore.
rustc: de-@ trans::_match.
rustc: de-@ ty::ParamBounds.
rustc: remove obsolete monomorphization modes.