Small fixups

- use `path` instead of `paths`
- don't mark rust-analyzer as an optional tool
- print the cargo command that's run in the proc-macro-test build script

  this originally was part of a change to fix `test --stage 0 rust-analyzer`,
  but I'm going to leave that for a separate PR so it's easier to review.

src/bootstrap/check.rs

@@ -312,7 +312,7 @@ impl Step for RustAnalyzer {
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
-        run.paths(&["src/tools/rust-analyzer"])
+        run.path("src/tools/rust-analyzer")
     }
 
     fn make_run(run: RunConfig<'_>) {

src/bootstrap/tool.rs

@@ -721,7 +721,7 @@ impl Step for RustAnalyzer {
             mode: Mode::ToolStd,
             path: "src/tools/rust-analyzer",
             extra_features: vec!["rust-analyzer/in-rust-tree".to_owned()],
-            is_optional_tool: true,
+            is_optional_tool: false,
             source_type: SourceType::InTree,
         })
     }