mir-opt: don't try other targets under --keep-stage-std

Author: Nadrieril

src/bootstrap/src/core/build_steps/test.rs

@@ -1551,7 +1551,9 @@ impl Step for MirOpt {
 
         run(self.target);
 
-        if builder.config.cmd.bless() {
+        // Run more targets on `--bless`, to try and cover all the tests. Don't try if we're keeping
+        // an std as that only makes sense for the current target.
+        if builder.config.cmd.bless() && builder.config.keep_stage_std.is_empty() {
             // All that we really need to do is cover all combinations of 32/64-bit and unwind/abort,
             // but while we're at it we might as well flex our cross-compilation support. This
             // selection covers all our tier 1 operating systems and architectures using only tier