TODO

- Consider adding makefiles to dist/ subdirectory for the following tests:

  cxx/hybrid/binary/custom
  cxx/hybrid/compositor
  cxx/hybrid/file-per-type
  cxx/hybrid/polymorphism/any-type
  cxx/hybrid/reorder
  cxx/hybrid/size
  cxx/parser/polyrecur
  cxx/serializer/generated-impl

- Fix undefined behavior when using enum variable which contain invalid value.
  Such issues are reported by the undefined behavior sanitizer as follows:

  xsde-examples/cxx/hybrid/compositors/compositors.cxx:182:13: runtime error: load of value 2, which is not a valid value for type 'choice_arm_tag'

  In such cases we intentionally assign invalid values to enum variable to
  indicate an absent value. One way to fix that is to use size_t type instead
  of enum for the variable and only cast to enum when it is supposed that the
  variable contains a valid enum value.

- Add build command lines to example README files.