Allow using -C force-unwind-tables=no when panic=unwind

src/test/assembly/panic-no-unwind-no-uwtable.rs

@@ -0,0 +1,8 @@
+// assembly-output: emit-asm
+// only-x86_64-unknown-linux-gnu
+// compile-flags: -C panic=unwind -C force-unwind-tables=n -O
+
+#![crate_type = "lib"]
+
+// CHECK-NOT: .cfi_startproc
+pub fn foo() {}

src/test/assembly/panic-unwind-no-uwtable.rs

@@ -0,0 +1,12 @@
+// assembly-output: emit-asm
+// only-x86_64-unknown-linux-gnu
+// compile-flags: -C panic=unwind -C force-unwind-tables=n
+
+#![crate_type = "lib"]
+
+// CHECK-LABEL: foo:
+// CHECK: .cfi_startproc
+#[no_mangle]
+fn foo() {
+    panic!();
+}

src/test/codegen/force-no-unwind-tables.rs

@@ -3,5 +3,9 @@
 
 #![crate_type="lib"]
 
+// CHECK-LABEL: define{{.*}}void @foo
 // CHECK-NOT: attributes #{{.*}} uwtable
-pub fn foo() {}
+#[no_mangle]
+fn foo() {
+    panic!();
+}

src/test/codegen/panic-unwind-default-uwtable.rs

@@ -0,0 +1,6 @@
+// compile-flags: -C panic=unwind -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+// CHECK: attributes #{{.*}} uwtable
+pub fn foo() {}

src/test/ui/panic-runtime/unwind-tables-panic-required.rs

@@ -1,10 +0,0 @@
-// Tests that the compiler errors if the user tries to turn off unwind tables
-// when they are required.
-//
-// dont-check-compiler-stderr
-// compile-flags: -C panic=unwind -C force-unwind-tables=no
-//
-// error-pattern: panic=unwind requires unwind tables, they cannot be disabled with `-C force-unwind-tables=no`.
-
-pub fn main() {
-}

src/test/ui/unwind-no-uwtable.rs

@@ -0,0 +1,34 @@
+// run-pass
+// ignore-windows target requires uwtable
+// ignore-wasm32-bare no proper panic=unwind support
+// compile-flags: -C panic=unwind -C force-unwind-tables=n
+
+use std::panic::{self, AssertUnwindSafe};
+
+struct Increase<'a>(&'a mut u8);
+
+impl Drop for Increase<'_> {
+    fn drop(&mut self) {
+        *self.0 += 1;
+    }
+}
+
+#[inline(never)]
+fn unwind() {
+    panic!();
+}
+
+#[inline(never)]
+fn increase(count: &mut u8) {
+    let _increase = Increase(count);
+    unwind();
+}
+
+fn main() {
+    let mut count = 0;
+    assert!(panic::catch_unwind(AssertUnwindSafe(
+        #[inline(never)]
+        || increase(&mut count)
+    )).is_err());
+    assert_eq!(count, 1);
+}