incr.comp.: Always verify incr. comp. hashes when running incremental tests.

Author: michaelwoerister

src/tools/compiletest/src/runtest.rs

@@ -1384,6 +1384,7 @@ actual:\n\
 
         if let Some(ref incremental_dir) = self.props.incremental_dir {
             rustc.args(&["-Z", &format!("incremental={}", incremental_dir.display())]);
+            rustc.args(&["-Z", "incremental-verify-ich"]);
         }
 
         match self.config.mode {