rewrite intrinsic-unreachable to rmake

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -47,7 +47,6 @@ run-make/foreign-rust-exceptions/Makefile
 run-make/incr-add-rust-src-component/Makefile
 run-make/incr-foreign-head-span/Makefile
 run-make/interdependent-c-libraries/Makefile
-run-make/intrinsic-unreachable/Makefile
 run-make/issue-107094/Makefile
 run-make/issue-109934-lto-debuginfo/Makefile
 run-make/issue-14698/Makefile

tests/run-make/intrinsic-unreachable/rmake.rs

@@ -0,0 +1,19 @@
+// intrinsics::unreachable tells the compiler that a certain point in the code
+// is not reachable by any means, which enables some useful optimizations.
+// In this test, exit-unreachable contains this instruction and exit-ret does not,
+// which means the emitted artifacts should be shorter in length.
+// See https://github.com/rust-lang/rust/pull/16970
+
+//@ needs-asm-support
+//@ ignore-windows-msvc
+// Reason: Because of Windows exception handling, the code is not necessarily any shorter.
+
+use run_make_support::rustc;
+use std::io::BufReader;
+use std::fs::File;
+
+fn main() {
+    rustc().opt().emit("asm").input("exit-ret.rs").run();
+    rustc().opt().emit("asm").input("exit-unreachable.rs").run();
+    assert!(BufReader::new(File::open("exit-unreachable.s")).lines().count() < BufReader::new(File::open("exit-ret.s")).lines().count());
+}