commit 2a6918e4fa57edbe0dc326d5f142350b1dd4afd7
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Aug 11 16:16:21 2020

    libstdc++: Make net::system_context tag type constructor explicit
    
    libstdc++-v3/ChangeLog:
    
            * include/experimental/executor (system_context::a__tag): Make
            default constructor explicit.

diff --git a/libstdc++-v3/include/experimental/executor b/libstdc++-v3/include/experimental/executor
index b5dc3035756..1561050ae23 100644
--- a/libstdc++-v3/include/experimental/executor
+++ b/libstdc++-v3/include/experimental/executor
@@ -884,7 +884,7 @@ inline namespace v1
   private:
     friend system_executor;
 
-    struct __tag { };
+    struct __tag { explicit __tag() = default; };
     system_context(__tag) { }
 
     thread			_M_thread;