Make the status messages emitted by bootstrap more clear

[jyn514]

I'm currently having an extended discussion in https://rust-lang.zulipchat.com/#narrow/stream/326414-t-infra.2Fbootstrap/topic/Stage.20numbering.20for.20tools about what the stage numbering for bootstrap means and how it should work. Part of the confusion, as pointed out by @the8472, is that it's unclear whether "Building stage1 std artifacts" refers to the compiler being run or the artifact being created. We should make this more clear by printing "Building stage1 std using stage0-sysroot".

(the names are kind of weird for now; #101961 will help with this.)

[jyn514]

This is "easy" but a lot of work; these messages are printed in a lot of different places across bootstrap and it's going to be a lot of manual work to update them all. #86022 had some WIP effort to make the status message autogenerated, but that will likely be even more work than updating the messages by hand.

[jyn514]

An example change:

diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 24b033cc0dc..b8ea072e584 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -70,7 +70,17 @@ fn run(self, builder: &Builder<'_>) -> Option<PathBuf> {
             &self.extra_features,
         );
 
-        builder.info(&format!("Building stage{} tool {} ({})", compiler.stage, tool, target));
+        let msg = if self.mode == Mode::ToolRustc {
+            format!(
+                "Building stage {} tool {tool} using stage {} sysroot ({target})",
+                compiler.stage + 1,
+                compiler.stage
+            )
+        } else {
+            format!("Building tool {tool} using stage {} sysroot ({target})", compiler.stage)
+        };
+        builder.info(&msg);
+
         let mut duplicates = Vec::new();
         let is_expected = compile::stream_cargo(builder, cargo, vec![], &mut |msg| {
             // Only care about big things like the RLS/Cargo for now

[jyn514]

fixed in #108171 (lol apparently i opened the same issue twice)