bootstrap: Allow ./x check compiletest

Author: Zalathar

src/bootstrap/src/core/build_steps/check.rs

@@ -501,6 +501,9 @@ tool_check_step!(
 );
 
 tool_check_step!(Bootstrap, "bootstrap", "src/bootstrap", SourceType::InTree, false);
+// Compiletest is implicitly "checked" when it gets built in order to run tests,
+// so this is mainly for people working on compiletest to run locally.
+tool_check_step!(Compiletest, "compiletest", "src/tools/compiletest", SourceType::InTree, false);
 
 /// Cargo's output path for the standard library in a given stage, compiled
 /// by a particular compiler for the specified target.

src/bootstrap/src/core/builder/mod.rs

@@ -905,6 +905,7 @@ impl<'a> Builder<'a> {
                 check::RustAnalyzer,
                 check::TestFloatParse,
                 check::Bootstrap,
+                check::Compiletest,
             ),
             Kind::Test => describe!(
                 crate::core::build_steps::toolstate::ToolStateCheck,