Call the panic hook for non-unwind panics in proc-macros

(cherry picked from commit d8dc28b)

Author: saethlin

library/proc_macro/src/bridge/client.rs

@@ -286,7 +286,11 @@ fn maybe_install_panic_hook(force_show_panics: bool) {
                 BridgeState::NotConnected => true,
                 BridgeState::Connected(_) | BridgeState::InUse => force_show_panics,
             });
-            if show {
+            // We normally report panics by catching unwinds and passing the payload from the
+            // unwind back to the compiler, but if the panic doesn't unwind we'll abort before
+            // the compiler has a chance to print an error. So we special-case PanicInfo where
+            // can_unwind is false.
+            if show || !info.can_unwind() {
                 prev(info)
             }
         }));

library/proc_macro/src/lib.rs

@@ -30,6 +30,7 @@
 #![feature(maybe_uninit_write_slice)]
 #![feature(negative_impls)]
 #![feature(new_uninit)]
+#![feature(panic_can_unwind)]
 #![feature(restricted_std)]
 #![feature(rustc_attrs)]
 #![feature(min_specialization)]