Revise C++ coding style using clang-format

Run the `Utilities/Scripts/clang-format.bash` script to update
all our C++ code to a new style defined by `.clang-format`.
Use `clang-format` version 3.8.

* 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/CompileFeatures/cxx_digit_separators.cpp

@@ -1,6 +1,5 @@
 
 int someFunc()
 {
-  int one_thousand = 1'000;
-  return one_thousand - 1000;
+  int one_thousand = 1'000; return one_thousand - 1000;
 }