[Driver] Preserve filelists when a subprocess crashes. (#9849)

This should make it easier to rerun crashed jobs that use filelists;
previously you'd have to run the top-level driver command again with
-save-temps. I didn't want to save /all/ temporary files because that
often includes things like .o files, which could fill up your disk
pretty quickly. But we can always tweak this later.

lib/Driver/ToolChain.cpp

@@ -57,7 +57,7 @@ ToolChain::JobContext::getTemporaryFilePath(const llvm::Twine &name,
     llvm::report_fatal_error("unable to create temporary file for filelist");
   }
 
-  C.addTemporaryFile(buffer.str());
+  C.addTemporaryFile(buffer.str(), PreserveOnSignal::Yes);
   // We can't just reference the data in the TemporaryFiles vector because
   // that could theoretically get copied to a new address.
   return C.getArgs().MakeArgString(buffer.str());