cmListCommand: Use std::find algorithm for FIND subcommand.

Use a ostringstream to account for the input being a variable of type
size_t as a result of using std::distance.  There is no single
format string which portably accepts a size_t.

Source/cmListCommand.cxx

@@ -284,18 +284,14 @@ bool cmListCommand::HandleFindCommand(std::vector<std::string> const& args)
     return true;
     }
 
-  std::vector<std::string>::iterator it;
-  unsigned int index = 0;
-  for ( it = varArgsExpanded.begin(); it != varArgsExpanded.end(); ++ it )
+  std::vector<std::string>::iterator it =
+      std::find(varArgsExpanded.begin(), varArgsExpanded.end(), args[2]);
+  if (it != varArgsExpanded.end())
     {
-    if ( *it == args[2] )
-      {
-      char indexString[32];
-      sprintf(indexString, "%d", index);
-      this->Makefile->AddDefinition(variableName, indexString);
-      return true;
-      }
-    index++;
+    std::ostringstream indexStream;
+    indexStream << std::distance(varArgsExpanded.begin(), it);
+    this->Makefile->AddDefinition(variableName, indexStream.str().c_str());
+    return true;
     }
 
   this->Makefile->AddDefinition(variableName, "-1");