For each link given as http://, verify that the site is accessible over
https:// and, if so, switch to it. These domains were converted:
* llvm.org
* clang.llvm.org
* en.cppreference.com
* www.dxx-rebirth.com
* www.libsdl.org
* www.scons.org
Future work will introduce uses of d1x/d2x in the other game when the
types can be usefully shared. Extend the anti-nesting guards to cover
mistakes that might arise when referring to the namespaces by their
real name, rather than the alias name dsx.