Remove all non-test usages of feature gates

ykrt/src/lib.rs

@@ -1,4 +1,3 @@
-#![feature(negative_impls)]
 #![cfg_attr(test, feature(test))]
 
 pub mod mt;

ykrt/src/mt.rs

@@ -243,11 +243,10 @@ type CompilingTrace<I> = Mutex<Option<Box<CompiledTrace<I>>>>;
 #[derive(Clone)]
 pub struct MTThread {
     inner: Rc<MTThreadInner>,
+    // Raw pointers are neither send nor sync.
+    _dont_send_or_sync_me: PhantomData<*mut ()>,
 }
 
-impl !Send for MTThread {}
-impl !Sync for MTThread {}
-
 impl MTThread {
     /// Return a meta-tracer [`MT`](struct.MT.html) struct.
     pub fn mt(&self) -> &MT {
@@ -491,6 +490,7 @@ impl MTThreadInner {
         };
         MTThread {
             inner: Rc::new(inner),
+            _dont_send_or_sync_me: PhantomData,
         }
     }
 }

yktrace/src/lib.rs

@@ -1,7 +1,7 @@
 #![cfg_attr(test, feature(test))]
-#![feature(thread_local)]
-#![feature(core_intrinsics)]
-#![feature(global_asm)]
+#![cfg_attr(tracermode = "sw", feature(thread_local))]
+#![cfg_attr(tracermode = "sw", feature(core_intrinsics))]
+#![cfg_attr(tracermode = "sw", feature(global_asm))]
 
 #[cfg(test)]
 extern crate test;