Rollup merge of #44717 - pnkfelix:debugflags-borrowckmir-implies-emitendregions, r=arielb1

Make `-Z borrowck-mir` imply that `EndRegion`'s should be emitted.

Before this change, the `-Z borrowck-mir` flag is useless if you do not also pass `-Z emit-end-regions`.

So, in the same spirit as f2892ad281, make `-Z borrowck-mir` also emit `EndRegion` statements. (This will hopefully avoid some initial speed bumps for new-comers helping out with NLL.)

src/librustc/session/mod.rs

@@ -411,7 +411,8 @@ pub fn print_llvm_passes(&self) -> bool {
     }
     pub fn emit_end_regions(&self) -> bool {
         self.opts.debugging_opts.emit_end_regions ||
-            (self.opts.debugging_opts.mir_emit_validate > 0)
+            (self.opts.debugging_opts.mir_emit_validate > 0) ||
+            self.opts.debugging_opts.borrowck_mir
     }
     pub fn lto(&self) -> bool {
         self.opts.cg.lto