Rollup merge of #125472 - erikdesjardins:component, r=clubby789

tidy: validate LLVM component names in tests

LLVM component names are not immediately obvious (they usually omit any suffixes on the target arch name), and if they're incorrect, the test will silently never run.

This happened [here](https://github.com/rust-lang/rust/pull/125220#discussion_r1612626002), and it would be nice to prevent it.

src/tools/tidy/src/target_specific_tests.rs

@@ -10,6 +10,25 @@ use crate::walk::filter_not_rust;
 const LLVM_COMPONENTS_HEADER: &str = "needs-llvm-components:";
 const COMPILE_FLAGS_HEADER: &str = "compile-flags:";
 
+const KNOWN_LLVM_COMPONENTS: &[&str] = &[
+    "aarch64",
+    "arm",
+    "avr",
+    "bpf",
+    "hexagon",
+    "loongarch",
+    "m68k",
+    "mips",
+    "msp430",
+    "nvptx",
+    "powerpc",
+    "riscv",
+    "sparc",
+    "systemz",
+    "webassembly",
+    "x86",
+];
+
 #[derive(Default, Debug)]
 struct RevisionInfo<'a> {
     target_arch: Option<&'a str>,
@@ -68,6 +87,17 @@ pub fn check(path: &Path, bad: &mut bool) {
                     // gathered.
                 }
             }
+            if let Some(llvm_components) = llvm_components {
+                for component in llvm_components {
+                    if !KNOWN_LLVM_COMPONENTS.contains(component) {
+                        eprintln!(
+                            "{}: revision {} specifies unknown LLVM component `{}`",
+                            file, rev, component
+                        );
+                        *bad = true;
+                    }
+                }
+            }
         }
     });
 }