Remove C++17 compilation error in fizz

Summary: C++17 deprecates declaration of constexpr static members, but seems it was not forced until Xcode 15.

Reviewed By: bricehalder

Differential Revision: D48610644

fbshipit-source-id: 7db31b8e788740b0a1366be8e40e874294ff4c2e

fizz/server/TicketCodec-inl.h

@@ -9,8 +9,12 @@
 namespace fizz {
 namespace server {
 
+// out-of-line definition of constexpr static data member is redundant in C++17
+// and is deprecated
+#if __cplusplus < 201703L
 template <CertificateStorage Storage>
 constexpr folly::StringPiece TicketCodec<Storage>::Label;
+#endif // __cplusplus < 201703L
 
 template <CertificateStorage Storage>
 Buf TicketCodec<Storage>::encode(ResumptionState resState) {