Improve diagnostic for unknown --print request

compiler/rustc_session/src/config.rs

@@ -1888,9 +1888,12 @@ fn collect_print_requests(
                 let prints =
                     PRINT_KINDS.iter().map(|(name, _)| format!("`{name}`")).collect::<Vec<_>>();
                 let prints = prints.join(", ");
-                early_dcx.early_fatal(format!(
-                    "unknown print request `{req}`. Valid print requests are: {prints}"
-                ));
+
+                let mut diag =
+                    early_dcx.early_struct_fatal(format!("unknown print request: `{req}`"));
+                #[allow(rustc::diagnostic_outside_of_impl)]
+                diag.help(format!("valid print requests are: {prints}"));
+                diag.emit()
             }
         };
 

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -317,7 +317,6 @@ run-make/unstable-flag-required/Makefile
 run-make/use-suggestions-rust-2018/Makefile
 run-make/used-cdylib-macos/Makefile
 run-make/used/Makefile
-run-make/valid-print-requests/Makefile
 run-make/volatile-intrinsics/Makefile
 run-make/wasm-exceptions-nostd/Makefile
 run-make/wasm-override-linker/Makefile

tests/run-make/valid-print-requests/Makefile

@@ -1,4 +0,0 @@
-include ../tools.mk
-
-all:
-	$(RUSTC) --print uwu 2>&1 | diff - valid-print-requests.stderr

tests/run-make/valid-print-requests/valid-print-requests.stderr

@@ -1,2 +0,0 @@
-error: unknown print request `uwu`. Valid print requests are: `all-target-specs-json`, `calling-conventions`, `cfg`, `code-models`, `crate-name`, `deployment-target`, `file-names`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `tls-models`
-

tests/ui/invalid-compile-flags/print.rs

@@ -0,0 +1 @@
+//@ compile-flags: --print yyyy

tests/ui/invalid-compile-flags/print.stderr

@@ -0,0 +1,4 @@
+error: unknown print request: `yyyy`
+  |
+  = help: valid print requests are: `all-target-specs-json`, `calling-conventions`, `cfg`, `code-models`, `crate-name`, `deployment-target`, `file-names`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `tls-models`
+