[Basic] Handle multiline strings in abortWithPrettyStackTraceMessage

Improve the formatting by indenting to match the rest of the
pretty stack trace.

lib/Basic/PrettyStackTrace.cpp

@@ -40,17 +40,38 @@ void PrettyStackTraceSwiftVersion::print(llvm::raw_ostream &out) const {
   out << version::getSwiftFullVersion() << '\n';
 }
 
+namespace {
+/// Similar to PrettyStackTraceString, but formats multi-line strings for
+/// the stack trace.
+class PrettyStackTraceMultilineString : public llvm::PrettyStackTraceEntry {
+  StringRef Str;
+
+public:
+  PrettyStackTraceMultilineString(StringRef str) : Str(str) {}
+  void print(raw_ostream &OS) const override {
+    // For each line, add a leading character and indentation to better match
+    // the formatting of the stack trace.
+    for (auto c : Str.rtrim('\n')) {
+      OS << c;
+      if (c == '\n')
+        OS << "| \t";
+    }
+    OS << '\n';
+  }
+};
+} // end anonymous namespace
+
 void swift::abortWithPrettyStackTraceMessage(
     llvm::function_ref<void(llvm::raw_ostream &)> message) {
   llvm::SmallString<0> errorStr;
   llvm::raw_svector_ostream out(errorStr);
   message(out);
-  llvm::PrettyStackTraceString trace(errorStr.c_str());
+
+  PrettyStackTraceMultilineString trace(errorStr);
   abort();
 }
 
 void swift::abortWithPrettyStackTraceMessage(StringRef message) {
-  auto messageStr = message.str();
-  llvm::PrettyStackTraceString trace(messageStr.c_str());
+  PrettyStackTraceMultilineString trace(message);
   abort();
 }