Rollup merge of #125047 - Oneirical:test5, r=jieyouxu

Migrate `run-make/issue-14500` to new `rmake.rs` format

Part of #121876 and the associated [Google Summer of Code project](https://blog.rust-lang.org/2024/05/01/gsoc-2024-selected-projects.html).

Note: I find suspicious that `libbar.a` is hardcoded and is not using the `STATICLIB` call to adapt to Windows platforms. Is this intentional? If not, this will need to be changed.

src/tools/run-make-support/src/rustc.rs

@@ -150,6 +150,19 @@ impl Rustc {
         self
     }
 
+    /// Enables link time optimizations in rustc. Equivalent to `-Clto``.
+    pub fn lto(&mut self) -> &mut Self {
+        self.cmd.arg("-Clto");
+        self
+    }
+
+    /// Add a directory to the library search path.
+    pub fn library_search_path<P: AsRef<Path>>(&mut self, path: P) -> &mut Self {
+        self.cmd.arg("-L");
+        self.cmd.arg(path.as_ref());
+        self
+    }
+
     /// Specify the edition year.
     pub fn edition(&mut self, edition: &str) -> &mut Self {
         self.cmd.arg("--edition");

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -95,7 +95,6 @@ run-make/issue-107094/Makefile
 run-make/issue-10971-temps-dir/Makefile
 run-make/issue-109934-lto-debuginfo/Makefile
 run-make/issue-11908/Makefile
-run-make/issue-14500/Makefile
 run-make/issue-14698/Makefile
 run-make/issue-15460/Makefile
 run-make/issue-18943/Makefile

tests/run-make/reachable-extern-fn-available-lto/rmake.rs

@@ -0,0 +1,26 @@
+// Test to make sure that reachable extern fns are always available in final
+// productcs, including when link time optimizations (LTO) are used.
+
+// In this test, the `foo` crate has a reahable symbol,
+// and is a dependency of the `bar` crate. When the `bar` crate
+// is compiled with LTO, it shouldn't strip the symbol from `foo`, and that's the
+// only way that `foo.c` will successfully compile.
+// See https://github.com/rust-lang/rust/issues/14500
+
+//@ ignore-cross-compile
+
+use run_make_support::{cc, extra_c_flags, run, rustc, static_lib, tmp_dir};
+
+fn main() {
+    let libbar_path = static_lib("bar");
+    rustc().input("foo.rs").crate_type("rlib").run();
+    rustc()
+        .input("bar.rs")
+        .crate_type("staticlib")
+        .lto()
+        .library_search_path(".")
+        .output(&libbar_path)
+        .run();
+    cc().input("foo.c").input(libbar_path).args(&extra_c_flags()).out_exe("foo").run();
+    run("foo");
+}