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.

Source/cmVisualStudioGeneratorOptions.cxx

@@ -393,7 +393,8 @@ void cmVisualStudioGeneratorOptions::StoreUnknownFlag(std::string const& flag)
 
   // This option is not known.  Store it in the output flags.
   std::string const opts = cmOutputConverter::EscapeWindowsShellArgument(
-    flag.c_str(), cmOutputConverter::Shell_Flag_AllowMakeVariables |
+    flag.c_str(),
+    cmOutputConverter::Shell_Flag_AllowMakeVariables |
       cmOutputConverter::Shell_Flag_VSIDE);
   this->AppendFlagString(this->UnknownFlagField, opts);
 }