std::uncaught_exception() -> std::uncaught_exceptions()

The former is deprecated in C++17. Fixes a clang warning.

src/libstore/remote-store.cc

@@ -228,7 +228,7 @@ struct ConnectionHandle
 
     ~ConnectionHandle()
     {
-        if (!daemonException && std::uncaught_exception()) {
+        if (!daemonException && std::uncaught_exceptions()) {
             handle.markBad();
             debug("closing daemon connection because of an exception");
         }

src/libutil/json.hh

@@ -170,7 +170,7 @@ public:
 
     ~JSONPlaceholder()
     {
-        assert(!first || std::uncaught_exception());
+        assert(!first || std::uncaught_exceptions());
     }
 
     template<typename T>

src/libutil/util.cc

@@ -1169,7 +1169,7 @@ void _interrupted()
     /* Block user interrupts while an exception is being handled.
        Throwing an exception while another exception is being handled
        kills the program! */
-    if (!interruptThrown && !std::uncaught_exception()) {
+    if (!interruptThrown && !std::uncaught_exceptions()) {
         interruptThrown = true;
         throw Interrupted("interrupted by the user");
     }