The minimum supported compiler versions now provide a depth-efficient
implementation of std::make_index_sequence, which removes the last
reason to carry a private implementation. In the case of clang, it
appears to have a special compiler intrinsic used to implement its
std::make_index_sequence.
Switch to the compiler-provided version for both gcc and clang.
gcc-4.9 support is now difficult to test due to system libraries linking
to newer symbols. gcc-4.9 is unsupported upstream, as are gcc-5 and
gcc-6. Raise the minimum required gcc version to the minimum version
supported upstream.
Debian Jessie shipped gcc-4.9.2, and support for this target was the
primary motivator for retaining gcc-4.9 support. Jessie ended regular
support in June 2018, and will end Long Term Support in June 2020. It
seems unlikely that Jessie would receive a snapshot build of Rebirth in
the months it has left.
Debian Stretch shipped gcc-6, but is currently considered "oldstable"
and has been superseded by Debian Buster. Further, Debian Stretch
provides a package for gcc-7, so Stretch users can still build Rebirth
using only packages available from the package manager.
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
Kp