Emit EndRegion statements when given -Z mir-emit-validate=N (for N > 0).

This way the miri test suite does not have to be updated to explcitly
request `-Z emit-end-regions`.

src/librustc/session/mod.rs

@@ -410,6 +410,10 @@ impl Session {
     pub fn print_llvm_passes(&self) -> bool {
         self.opts.debugging_opts.print_llvm_passes
     }
+    pub fn emit_end_regions(&self) -> bool {
+        self.opts.debugging_opts.emit_end_regions ||
+            (self.opts.debugging_opts.mir_emit_validate > 0)
+    }
     pub fn lto(&self) -> bool {
         self.opts.cg.lto
     }

src/librustc_mir/build/cfg.rs

@@ -50,7 +50,7 @@ impl<'tcx> CFG<'tcx> {
                                              block: BasicBlock,
                                              source_info: SourceInfo,
                                              region_scope: region::Scope) {
-        if tcx.sess.opts.debugging_opts.emit_end_regions {
+        if tcx.sess.emit_end_regions() {
             self.push(block, Statement {
                 source_info,
                 kind: StatementKind::EndRegion(region_scope),

src/librustc_mir/transform/clean_end_regions.rs

@@ -42,7 +42,7 @@ impl MirPass for CleanEndRegions {
                           tcx: TyCtxt<'a, 'tcx, 'tcx>,
                           _source: MirSource,
                           mir: &mut Mir<'tcx>) {
-        if !tcx.sess.opts.debugging_opts.emit_end_regions { return; }
+        if !tcx.sess.emit_end_regions() { return; }
 
         let mut gather = GatherBorrowedRegions {
             seen_regions: FxHashSet()