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/cmGhsMultiTargetGenerator.h

@@ -3,14 +3,14 @@
 #ifndef cmGhsMultiTargetGenerator_h
 #define cmGhsMultiTargetGenerator_h
 
-#include "cmGhsMultiGpj.h"
-
 #include <iosfwd>
 #include <map>
 #include <set>
 #include <string>
 #include <vector>
 
+#include "cmGhsMultiGpj.h"
+
 class cmCustomCommand;
 class cmCustomCommandGenerator;
 class cmGeneratorTarget;