rewrite extern-fn-generic to rmake

Author: Oneirical

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -26,7 +26,6 @@ run-make/export-executable-symbols/Makefile
 run-make/extern-diff-internal-name/Makefile
 run-make/extern-flag-disambiguates/Makefile
 run-make/extern-fn-explicit-align/Makefile
-run-make/extern-fn-generic/Makefile
 run-make/extern-fn-mangle/Makefile
 run-make/extern-fn-reachable/Makefile
 run-make/extern-fn-struct-passing-abi/Makefile

tests/run-make/extern-fn-generic/Makefile

@@ -0,0 +1,15 @@
+// Generic types in foreign-function interfaces were introduced in #15831 - this
+// test simply runs a Rust program containing generics that is also reliant on
+// a C library, and checks that compilation and execution are successful.
+// See https://github.com/rust-lang/rust/pull/15831
+//@ ignore-cross-compile
+// Reason: the compiled binary is executed
+
+use run_make_support::{build_native_static_lib, run, rustc};
+
+fn main() {
+    build_native_static_lib("test");
+    rustc().input("testcrate.rs").run();
+    rustc().input("test.rs").run();
+    run("test");
+}