Revise include order using clang-format-6.0

Run the `clang-format.bash` script to update our C and C++ code to a new
include order `.clang-format`.  Use `clang-format` version 6.0.

Source/cmFileAPICMakeFiles.cxx

@@ -2,6 +2,11 @@
    file Copyright.txt or https://cmake.org/licensing for details.  */
 #include "cmFileAPICMakeFiles.h"
 
+#include <string>
+#include <vector>
+
+#include "cm_jsoncpp_value.h"
+
 #include "cmFileAPI.h"
 #include "cmGlobalGenerator.h"
 #include "cmLocalGenerator.h"
@@ -9,11 +14,6 @@
 #include "cmSystemTools.h"
 #include "cmake.h"
 
-#include "cm_jsoncpp_value.h"
-
-#include <string>
-#include <vector>
-
 namespace {
 
 class CMakeFiles