rustbuild: Skip some more non-relevant dist steps

This commit skips a few more dist tragets during compilation which shouldn't be
necessary.

* First, when packaging std we only take action when the host target is the
  build target. Otherwise we package the same artifacts a number of times, which
  shouldn't be necessary.
* Next, we apply the same logic to the save-analysis build. This is actually
  required for correctness as the build compiler is the only one which actually
  has save analysis information. This should fix an error seen on nightlies.

src/bootstrap/dist.rs

@@ -260,6 +260,14 @@ pub fn debugger_scripts(build: &Build,
 pub fn std(build: &Build, compiler: &Compiler, target: &str) {
     println!("Dist std stage{} ({} -> {})", compiler.stage, compiler.host,
              target);
+
+    // The only true set of target libraries came from the build triple, so
+    // let's reduce redundant work by only producing archives from that host.
+    if compiler.host != build.config.build {
+        println!("\tskipping, not a build host");
+        return
+    }
+
     let name = format!("rust-std-{}", package_vers(build));
     let image = tmpdir(build).join(format!("{}-{}-image", name, target));
     let _ = fs::remove_dir_all(&image);
@@ -294,10 +302,15 @@ pub fn analysis(build: &Build, compiler: &Compiler, target: &str) {
     println!("Dist analysis");
 
     if build.config.channel != "nightly" {
-        println!("Skipping dist-analysis - not on nightly channel");
+        println!("\tskipping - not on nightly channel");
         return;
     }
+    if compiler.host != build.config.build {
+        println!("\tskipping - not a build host");
+        return
+    }
     if compiler.stage != 2 {
+        println!("\tskipping - not stage2");
         return
     }