Consolidate header inclusion diagnostics

Make argument orders match, unify diagnostic IDs and reword the message to be a
little less saccharine.

llvm-svn: 212845
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index f7d5623..976f3a6 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -3867,7 +3867,8 @@
   if (!EmitHeaderHint)
     return;
 
-  S.Diag(Loc, diag::note_please_include_header) << HeaderName << FunctionName;
+  S.Diag(Loc, diag::note_include_header_or_declare) << HeaderName
+                                                    << FunctionName;
 }
 
 static bool IsFunctionStdAbs(const FunctionDecl *FDecl) {
@@ -3907,8 +3908,8 @@
   QualType ArgType = Call->getArg(0)->IgnoreParenImpCasts()->getType();
   QualType ParamType = Call->getArg(0)->getType();
 
-  // Unsigned types can not be negative.  Suggest to drop the absolute value
-  // function.
+  // Unsigned types cannot be negative.  Suggest removing the absolute value
+  // function call.
   if (ArgType->isUnsignedIntegerType()) {
     const char *FunctionName =
         IsStdAbs ? "std::abs" : Context.BuiltinInfo.GetName(AbsKind);