[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.

include/swift/Driver/Compilation.h

@@ -57,6 +57,13 @@ enum class OutputLevel {
   Parseable,
 };
 
+/// Indicates whether a temporary file should always be preserved if a part of
+/// the compilation crashes.
+enum class PreserveOnSignal : bool {
+  No,
+  Yes
+};
+
 class Compilation {
   friend class PerformJobsState;
 private:
@@ -87,8 +94,8 @@ private:
 
   /// Temporary files that should be cleaned up after the compilation finishes.
   ///
-  /// These apply whether the compilation succeeds or fails.
-  std::vector<std::string> TempFilePaths;
+  /// These apply whether the compilation succeeds or fails. If the
+  llvm::StringMap<PreserveOnSignal> TempFilePaths;
 
   /// Write information about this compilation to this file.
   ///
@@ -174,14 +181,13 @@ public:
   }
   Job *addJob(std::unique_ptr<Job> J);
 
-  void addTemporaryFile(StringRef file) {
-    TempFilePaths.push_back(file.str());
+  void addTemporaryFile(StringRef file,
+                        PreserveOnSignal preserve = PreserveOnSignal::No) {
+    TempFilePaths[file] = preserve;
   }
 
   bool isTemporaryFile(StringRef file) {
-    // TODO: Use a set instead of a linear search.
-    return std::find(TempFilePaths.begin(), TempFilePaths.end(), file) !=
-             TempFilePaths.end();
+    return TempFilePaths.count(file);
   }
 
   const llvm::opt::DerivedArgList &getArgs() const { return *TranslatedArgs; }
@@ -255,9 +261,12 @@ public:
 private:
   /// \brief Perform all jobs.
   ///
-  /// \returns exit code of the first failed Job, or 0 on success. A return
-  /// value of -2 indicates that a Job crashed during execution.
-  int performJobsImpl();
+  /// \param[out] abnormalExit Set to true if any job exits abnormally (i.e.
+  /// crashes).
+  ///
+  /// \returns exit code of the first failed Job, or 0 on success. If a Job
+  /// crashes during execution, a negative value will be returned.
+  int performJobsImpl(bool &abnormalExit);
 
   /// \brief Performs a single Job by executing in place, if possible.
   ///