Add test for unwinding past terminating POF

tests/run-make/forced-unwind-terminate-pof/Makefile

@@ -0,0 +1,9 @@
+# ignore-cross-compile
+# only-linux
+include ../tools.mk
+
+all: foo
+	$(call RUN,foo) | $(CGREP) -v "cannot unwind"
+
+foo: foo.rs
+	$(RUSTC) $<

tests/run-make/forced-unwind-terminate-pof/foo.rs

@@ -0,0 +1,17 @@
+// Tests that forced unwind through POF Rust frames wouldn't trigger our terminating guards.
+
+#![feature(c_unwind)]
+#![no_main]
+
+extern "C-unwind" {
+    fn pthread_exit(v: *mut core::ffi::c_void) -> !;
+}
+
+unsafe extern "C" fn call_pthread_exit() {
+    pthread_exit(core::ptr::null_mut());
+}
+
+#[no_mangle]
+unsafe extern "C-unwind" fn main(_argc: core::ffi::c_int, _argv: *mut *mut core::ffi::c_char) {
+    call_pthread_exit();
+}