Since this should never be invoked, simplify the definition. The new
version is slightly less informative in case a logic error causes it to
be called, but is far shorter and easier to understand.
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