Guidelines: Guidelines in use of #ifdef in C/C++ programs.
Projects: GCC, Gnome, Hurd, Gimp, Inkscape, Linux, Libreoffice, Firefox, Wireshark
Bugs/Guidelines description by colors:

guideline3
  1. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41465 (bug54)
  2. https://bugzilla.gnome.org/show_bug.cgi?id=142749
  3. https://bugzilla.gnome.org/show_bug.cgi?id=541413
  4. https://www.libreoffice.org/bugzilla/show_bug.cgi?id=2370
  5. https://bugzilla.mozilla.org/show_bug.cgi?id=807161
  6. https://bugzilla.mozilla.org/show_bug.cgi?id=577915
  7. https://bugzilla.mozilla.org/show_bug.cgi?id=774120
  8. https://bugzilla.gnome.org/show_bug.cgi?id=342406
  9. https://bugzilla.gnome.org/show_bug.cgi?id=580750
  10. http://lists.gnu.org/archive/html/bug-hurd/2011-09/msg00086.html
  11. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43936
  12. https://www.libreoffice.org/bugzilla/show_bug.cgi?id=3118
  13. https://bugzilla.gnome.org/show_bug.cgi?id=728370
  14. https://bugzilla.mozilla.org/show_bug.cgi?id=a
  15. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47571
  16. https://git.gnome.org/browse/libxml2/commit/?id=41586ca6674d2fae32b17156494cb6f244ac1170
  17. https://git.gnome.org/browse/libxml2/commit/?id=52010c639a5da3d40ef73d9aff5c43c3a642661c
  18. https://git.gnome.org/browse/libxml2/commit/?id=0c7109c81f3de1408ddac898bce0aa21823e3507
  19. https://git.gnome.org/browse/libxml2/commit/?id=3313d14f9d71e5beeb51169688b69f3a34fe4489
  20. https://git.gnome.org/browse/libgda/commit/?id=e4820b869a088c7cf5328ff4d7a7f5caf36e5e33
  21. https://git.gnome.org/browse/libgda/commit/?id=deea473d2ebbc5c61968ee088b91d3ca650df478
  22. https://git.gnome.org/browse/libgda/commit/?id=449780910651ee2f551ed795880bafda62ee582f
  23. https://git.gnome.org/browse/gtk+/commit/?id=1c099ec78489ac29a74cfcbdb953f7282652d72b
  24. https://git.gnome.org/browse/nautilus/commit/?id=bf8571a78f1f8c73ea449e56fa413abb3f40b91c
  25. http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=f48ec1d7885281a9c6cd7779d61f321d1b1fd741