Revise C++ coding style using clang-format-6.0

Run the `clang-format.bash` script to update all our C and C++ code to a
new style defined by `.clang-format`.  Use `clang-format` version 6.0.

* If you reached this commit for a line in `git blame`, re-run the blame
  operation starting at the parent of this commit to see older history
  for the content.

* See the parent commit for instructions to rebase a change across this
  style transition commit.

Tests/ComplexOneConfig/Executable/complex.file.cxx

@@ -1,5 +1,5 @@
 #if 0
-#include "cmMissingHeader.h"
+#  include "cmMissingHeader.h"
 #endif
 
 int main(int, char**)