-Rename -Wargument-larger-than -> -Wlarge-by-value-copy
-Improve the diagnostic message
-Add some comments

Suggestions by Chris.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@119594 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index d9e3760..60d2fe3 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -1199,13 +1199,13 @@
     CmdArgs.push_back(A->getValue(Args));
   }
 
-  if (Arg *A = Args.getLastArg(options::OPT_Wargument_larger_than_EQ,
-                               options::OPT_Wargument_larger_than_def)) {
-    CmdArgs.push_back("-Wargument-larger-than");
+  if (Arg *A = Args.getLastArg(options::OPT_Wlarge_by_value_copy_EQ,
+                               options::OPT_Wlarge_by_value_copy_def)) {
+    CmdArgs.push_back("-Wlarge-by-value-copy");
     if (A->getNumValues())
       CmdArgs.push_back(A->getValue(Args));
     else
-      CmdArgs.push_back("64"); // default value for -Wargument-larger-than
+      CmdArgs.push_back("64"); // default value for -Wlarge-by-value-copy.
   }
 
   if (Args.hasArg(options::OPT__relocatable_pch))