rewrite target-cpu-native to rmake

Author: Oneirical

tests/run-make/target-cpu-native/Makefile

@@ -0,0 +1,16 @@
+// target-cpu is a codegen flag that generates code for the processor of the host machine
+// running the compilation. This test is a sanity test that this flag does not cause any
+// warnings when used, and that binaries produced by it can also be successfully executed.
+// See https://github.com/rust-lang/rust/pull/23238
+
+// FIXME(Oneirical): only-linux only-x86_64
+
+use run_make_support::{run, rustc};
+
+fn main() {
+    let out = rustc().input("foo.rs").arg("-Ctarget-cpu=native").run().stderr_utf8();
+    run("foo");
+    // There should be zero warnings emitted - the bug would cause "unknown CPU `native`"
+    // to be printed out.
+    assert_eq!(out.len(), 0);
+}