Make sure that `#include <cmConfigure.h>` is followed by an empty line
in header files.  This is necessary to make sure that changing <> to ""
does not affect the include ordering of clang-format.

Automate with:

git grep -l '#include <cmConfigure.h>' | grep -v '.cxx$' \
| xargs sed -i '/#include <cmConfigure.h>/ { N; N; s/\n\{1,2\}/\n\n/ }'