Avoid explicit memset in IPAddress storage union

Summary: [Folly] Avoid explicit `memset` in `IPAddress` storage union by having an explicit storage field and value-initializing it in the default constructor.

Reviewed By: stevegury

Differential Revision: D14270246

fbshipit-source-id: f1f135f20709d8225e984ee3d6b397d4b04e0d76

folly/IPAddress.h

@@ -442,12 +442,11 @@ class IPAddress {
   [[noreturn]] void asV6Throw() const;
 
   typedef union IPAddressV46 {
+    std::aligned_union_t<0, IPAddressV4, IPAddressV6> storage;
     IPAddressV4 ipV4Addr;
     IPAddressV6 ipV6Addr;
     // default constructor
-    IPAddressV46() noexcept {
-      std::memset(this, 0, sizeof(IPAddressV46));
-    }
+    IPAddressV46() noexcept : storage() {}
     explicit IPAddressV46(const IPAddressV4& addr) noexcept : ipV4Addr(addr) {}
     explicit IPAddressV46(const IPAddressV6& addr) noexcept : ipV6Addr(addr) {}
   } IPAddressV46;