[Serialization] Fix crash in reporting missing implementationOnly modules

The diagnostic function crashed as it did not take into account the
DebuggerSupport options as the site reporting the missing dependency did.
In this context, missing implementation-only imported dependencies are
ignored only if DebuggerSupport is set.

Author: xymus

lib/Serialization/SerializedModuleLoader.cpp

@@ -738,9 +738,10 @@ void swift::serialization::diagnoseSerializedASTLoadFailure(
     std::copy_if(
         loadedModuleFile->getDependencies().begin(),
         loadedModuleFile->getDependencies().end(), std::back_inserter(missing),
-        [&duplicates](const ModuleFile::Dependency &dependency) -> bool {
+        [&duplicates, &Ctx](const ModuleFile::Dependency &dependency) -> bool {
           if (dependency.isLoaded() || dependency.isHeader() ||
-              dependency.isImplementationOnly()) {
+              (dependency.isImplementationOnly() &&
+               Ctx.LangOpts.DebuggerSupport)) {
             return false;
           }
           return duplicates.insert(dependency.RawPath).second;