CppParser: fix compilation warnings

Fix the compilation warnings with gcc:

../../../src/CppParser/Parser.cpp: In member function ‘CppSharp::CppParser::AST::DeclarationContext*
 CppSharp::CppParser::Parser::GetNamespace(clang::Decl*, clang::DeclContext*)’:
../../../src/CppParser/Parser.cpp:1119:68: warning: format ‘%s’ expects argument of type ‘char*’, but argument 2 has type ‘llvm::StringRef’ [-Wformat=]
             printf("Unhandled declaration context kind: %s\n", Kind);
                                                                    ^
../../../src/CppParser/Parser.cpp: In member function ‘CppSharp::CppParser::AST::Declaration* CppSharp::CppParser::Parser::WalkDeclaration(clang::Decl*, bool, bool)’:
../../../src/CppParser/Parser.cpp:2430:51: warning: format ‘%s’ expects argument of type ‘char*’, but argument 2 has type ‘llvm::StringRef’ [-Wformat=]
         Debug("  %s (line %u)\n", FileName, LineNo);
                                                   ^

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@iki.fi>

src/CppParser/Parser.cpp

@@ -1126,7 +1126,7 @@ DeclarationContext* Parser::GetNamespace(clang::Decl* D,
         default:
         {
             StringRef Kind = Ctx->getDeclKindName();
-            printf("Unhandled declaration context kind: %s\n", Kind);
+            printf("Unhandled declaration context kind: %s\n", Kind.str().c_str());
             assert(0 && "Unhandled declaration context kind");
         } }
     }
@@ -2456,7 +2456,7 @@ Declaration* Parser::WalkDeclaration(clang::Decl* D,
         auto FileName = SM.getFilename(Loc);
         auto Offset = SM.getFileOffset(Loc);
         auto LineNo = SM.getLineNumber(SM.getFileID(Loc), Offset);
-        Debug("  %s (line %u)\n", FileName, LineNo);
+        Debug("  %s (line %u)\n", FileName.str().c_str(), LineNo);
 
         break;
     } };