Add migrate to list of values for -Z borrowck=...

Author: pnkfelix

src/librustc/session/config.rs

@@ -1141,7 +1141,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
     emit_end_regions: bool = (false, parse_bool, [UNTRACKED],
         "emit EndRegion as part of MIR; enable transforms that solely process EndRegion"),
     borrowck: Option<String> = (None, parse_opt_string, [UNTRACKED],
-        "select which borrowck is used (`ast`, `mir`, or `compare`)"),
+        "select which borrowck is used (`ast`, `mir`, `migrate`, or `compare`)"),
     two_phase_borrows: bool = (false, parse_bool, [UNTRACKED],
         "use two-phase reserved/active distinction for `&mut` borrows in MIR borrowck"),
     two_phase_beyond_autoref: bool = (false, parse_bool, [UNTRACKED],