Add CopyDiagnostic to the DiagnosticManager.

From Gregor Milos (gmilos@apple.com), for:

https://reviews.llvm.org/D32078

llvm-svn: 300733
diff --git a/lldb/source/Expression/DiagnosticManager.cpp b/lldb/source/Expression/DiagnosticManager.cpp
index 5ade081..ae20feb 100644
--- a/lldb/source/Expression/DiagnosticManager.cpp
+++ b/lldb/source/Expression/DiagnosticManager.cpp
@@ -79,3 +79,12 @@
   AddDiagnostic(str, severity, eDiagnosticOriginLLDB);
   return str.size();
 }
+
+void DiagnosticManager::CopyDiagnostics(DiagnosticManager &otherDiagnostics) {
+  for (const DiagnosticList::value_type &other_diagnostic:
+       otherDiagnostics.Diagnostics()) {
+    AddDiagnostic(
+        other_diagnostic->GetMessage(), other_diagnostic->GetSeverity(),
+        other_diagnostic->getKind(), other_diagnostic->GetCompilerID());
+  }
+}