Rename Diagnostic to DiagnosticsEngine as per issue 5397


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@140478 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/Preprocessor.cpp b/lib/Lex/Preprocessor.cpp
index 8c1004b..2937b60 100644
--- a/lib/Lex/Preprocessor.cpp
+++ b/lib/Lex/Preprocessor.cpp
@@ -49,7 +49,7 @@
 //===----------------------------------------------------------------------===//
 ExternalPreprocessorSource::~ExternalPreprocessorSource() { }
 
-Preprocessor::Preprocessor(Diagnostic &diags, LangOptions &opts,
+Preprocessor::Preprocessor(DiagnosticsEngine &diags, LangOptions &opts,
                            const TargetInfo *target, SourceManager &SM,
                            HeaderSearch &Headers, ModuleLoader &TheModuleLoader,
                            IdentifierInfoLookup* IILookup,