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
Fallback support for Boost.Foreach is broken and no one has reported it.
The minimum required gcc version supports range-based for. Recent Clang
supports range-based for. No Microsoft compilers are supported. Remove
support for the fallback Boost.Foreach and move the C++11 range-based
for test to the Cxx11RequiredFeature array.