[RemoteMirrors] Fix losing the remote address on StaticMirror

The Offset field of a DynamicRelocation is either an offset or a remote
address, but was being treated only as a remote address on
getDynamicSymbol.

include/swift/StaticMirror/ObjectFileContext.h

@@ -39,8 +39,12 @@ private:
   uint64_t HeaderAddress;
   std::vector<Segment> Segments;
   struct DynamicRelocation {
+    /// The symbol name that the pointer refers to. Empty if only an absolute
+    /// address is available.
     StringRef Symbol;
-    uint64_t Offset;
+    // The offset (if the symbol is available), or the resolved remote address
+    // if the symbol is empty.
+    uint64_t OffsetOrAddress;
   };
   llvm::DenseMap<uint64_t, DynamicRelocation> DynamicRelocations;