Two void functions that should not have return statements.

(Proper) C doesn't let you tail-call a void returning function.
gcc lets you get away with this.

src/core/index_hash_table.c

@@ -302,5 +302,5 @@ void MVM_index_hash_insert_nocheck(MVMThreadContext *tc,
             hashtable->table = control = new_control;
         }
     }
-    return hash_insert_internal(tc, control, list, idx);
+    hash_insert_internal(tc, control, list, idx);
 }

src/core/threadcontext.h

@@ -369,7 +369,7 @@ MVM_STATIC_INLINE MVMThreadContext *MVM_get_running_threads_context(void) {
 }
 
 MVM_STATIC_INLINE void MVM_set_running_threads_context(MVMThreadContext *tc) {
-    return uv_key_set(&MVM_running_threads_context_key, tc);
+    uv_key_set(&MVM_running_threads_context_key, tc);
 }
 
 #endif