Update cpplint support to return 0 and mark warnings for CDash.

This commit makes cpplint act like the other compiler mirroring tools. It
will always return 0 even if it reports warnings and will only return non
zero if there is a problem running the command. In addition, it will now
add some extra text to allow CTest to recognize the warnings and report
them correctly to CDash.

Source/cmcmd.cxx

@@ -270,10 +270,12 @@ static int HandleCppLint(const std::string& runCmd,
               << "\n";
     return 1;
   }
-
+  std::cerr << "Warning: cpplint diagnostics:\n";
   // Output the output from cpplint to stderr
   std::cerr << stdOut;
-  return ret;
+  // always return 0 so the build can continue as cpplint returns non-zero
+  // for any warning
+  return 0;
 }
 
 static int HandleCppCheck(const std::string& runCmd,

Tests/RunCMake/Cpplint/C-error-Build-result.txt

@@ -1 +1 @@
-[^0]
+0

Tests/RunCMake/Cpplint/C-error-launch-Build-result.txt

@@ -1 +1 @@
-[^0]
+0

Tests/RunCMake/Cpplint/CXX-error-Build-result.txt

@@ -1 +1 @@
-[^0]
+0

Tests/RunCMake/Cpplint/CXX-error-launch-Build-result.txt

@@ -1 +1 @@
-[^0]
+0