Replace absl::variant constructor call with emplace to fix clang10 compilation error.

Verified the fix compiles by compiling envoy with clang10.

PiperOrigin-RevId: 341628716
Change-Id: Ide0ef47926a7fb2df6bd7420345660f265bca352

quic/core/quic_unacked_packet_map.h

diff --git a/quic/core/quic_unacked_packet_map.h b/quic/core/quic_unacked_packet_map.h
index a6c0025..4541351 100644
--- a/quic/core/quic_unacked_packet_map.h
+++ b/quic/core/quic_unacked_packet_map.h
@@ -118,8 +118,12 @@
   template <typename Itr1, typename Itr2>
   class QUIC_EXPORT_PRIVATE IteratorWrapper {
    public:
-    explicit IteratorWrapper(Itr1 itr1) : itr_(std::move(itr1)) {}
-    explicit IteratorWrapper(Itr2 itr2) : itr_(std::move(itr2)) {}
+    explicit IteratorWrapper(Itr1 itr1) {
+      itr_.template emplace<0>(std::move(itr1));
+    }
+    explicit IteratorWrapper(Itr2 itr2) {
+      itr_.template emplace<1>(std::move(itr2));
+    }
 
     auto& operator*() const {
       return absl::visit(