Modified the internals of Diagnostic and DiagnosticClient to use
SourceManager*'s instead of SourceManager&'s. This allows the client specify a
NULL SourceManager when using a default constructed SourceLocation. Thus the
SourceManager can be NULL when the SourceLocation's isValid() == false.

The interface to most clients of Diagnostic remains the same.
Diagnostic::Report() is overload to either accept a SourceLocation and a
SourceManager&, or neither. Thus clients that do not have a SourceManager
cannot specify a SourceLocation.

Modified TextDiagnostics* to use this new interface.
Modified the driver to not passed in SourceManager when warning about "-I-".


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@44887 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Driver/TextDiagnosticBuffer.h b/Driver/TextDiagnosticBuffer.h
index 5da37c3..53a6cb7 100644
--- a/Driver/TextDiagnosticBuffer.h
+++ b/Driver/TextDiagnosticBuffer.h
@@ -41,7 +41,7 @@
   virtual void HandleDiagnostic(Diagnostic &Diags, Diagnostic::Level DiagLevel,
                                 SourceLocation Pos,
                                 diag::kind ID,
-                                SourceManager& SrcMgr,
+                                SourceManager* SrcMgr,
                                 const std::string *Strs,
                                 unsigned NumStrs,
                                 const SourceRange *Ranges,