Fix Clang-tidy modernize-use-nullptr warnings in examples and include directories; other minor cleanups.

Patch by Eugene Zelenko!

Differential Revision: http://reviews.llvm.org/D13172

llvm-svn: 248811
diff --git a/llvm/examples/Kaleidoscope/Chapter4/toy.cpp b/llvm/examples/Kaleidoscope/Chapter4/toy.cpp
index 8c96444..4f77ec8 100644
--- a/llvm/examples/Kaleidoscope/Chapter4/toy.cpp
+++ b/llvm/examples/Kaleidoscope/Chapter4/toy.cpp
@@ -65,7 +65,7 @@
       LastChar = getchar();
     } while (isdigit(LastChar) || LastChar == '.');
 
-    NumVal = strtod(NumStr.c_str(), 0);
+    NumVal = strtod(NumStr.c_str(), nullptr);
     return tok_number;
   }
 
@@ -200,6 +200,7 @@
   fprintf(stderr, "Error: %s\n", Str);
   return nullptr;
 }
+
 std::unique_ptr<PrototypeAST> ErrorP(const char *Str) {
   Error(Str);
   return nullptr;