Merge pull request #16472 from mikeash/silence-offsetof-warning

[Runtime] Silence warnings for offsetof usage on TupleCacheEntry.

Author: mikeash

stdlib/public/runtime/Metadata.cpp

@@ -876,6 +876,9 @@ class TupleCacheEntry
 
 class TupleCache : public MetadataCache<TupleCacheEntry, false, TupleCache> {
 public:
+// FIXME: https://bugs.swift.org/browse/SR-1155
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Winvalid-offsetof"
   static TupleCacheEntry *
   resolveExistingEntry(const TupleTypeMetadata *metadata) {
     // The correctness of this arithmetic is verified by an assertion in
@@ -885,6 +888,7 @@ class TupleCache : public MetadataCache<TupleCacheEntry, false, TupleCache> {
     auto entry = reinterpret_cast<const TupleCacheEntry*>(bytes);
     return const_cast<TupleCacheEntry*>(entry);
   }
+#pragma clang diagnostic pop
 };
 
 } // end anonymous namespace