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,
         })
     }

src/tools/rust-analyzer/crates/proc-macro-test/build.rs

@@ -62,7 +62,7 @@ fn main() {
         Command::new(toolchain::cargo())
     };
 
-    let output = cmd
+    cmd
         .current_dir(&staging_dir)
         .args(&["build", "-p", "proc-macro-test-impl", "--message-format", "json"])
         // Explicit override the target directory to avoid using the same one which the parent
@@ -70,9 +70,11 @@ fn main() {
         // This can happen when `CARGO_TARGET_DIR` is set or global config forces all cargo
         // instance to use the same target directory.
         .arg("--target-dir")
-        .arg(&target_dir)
-        .output()
-        .unwrap();
+        .arg(&target_dir);
+
+    println!("Running {:?}", cmd);
+
+    let output = cmd.output().unwrap();
     if !output.status.success() {
         println!("proc-macro-test-impl failed to build");
         println!("============ stdout ============");