[Serialization] Do not 'stat' SDK-relative dependencies when collecting serialization deps

Author: artemcm

lib/Frontend/ModuleInterfaceBuilder.cpp

@@ -148,11 +148,15 @@ bool ExplicitModuleInterfaceBuilder::collectDepsForSerialization(
     if (DepName.starts_with(ResourcePath))
       continue;
 
-    auto Status = fs.status(DepName);
-    if (!Status) {
-      Instance.getDiags().diagnose(SourceLoc(), diag::cannot_open_file, DepName,
-                                   Status.getError().message());
-      return true;
+    // Only validate non-sdk-relative inputs. Querying sdk-relative inputs
+    // should not be necessary.
+    if (!IsSDKRelative) {
+      auto Status = fs.status(DepName);
+      if (!Status) {
+        Instance.getDiags().diagnose(SourceLoc(), diag::cannot_open_file, DepName,
+                                     Status.getError().message());
+        return true;
+      }
     }
 
     /// Lazily load the dependency buffer if we need it. If we're not