[CMake] CMake update for older PPC7

[Mojca Miklavec]

On 23 June 2018 at 17:45, Gregor Jasny via CMake wrote:
>
> 2) Compile it yourself. CMake is self-contained so compilation should be
> relatively easy. Please note that latest versions depend on a C++11
> compatible toolchain. There is a boostrap script to compile CMake
> without CMake and break the dependency cycle.

Speaking of dependency cycles ... we do have quite a bit of troubles
with CMake on a package manager on legacy Mac OS X platforms. C++11
means that one needs a recent and decent compiler, but the latest
clang and libc++ both require CMake to be built.

There are some workarounds that require building several versions of
clang (I think it's all of clang 3.3, 3.4, 3,7 and then the latest
one; libc++ has not been updated yet just because nobody dares to
touch it, to a big part due to dependency on CMake) just for the sake
of avoiding dependency cycles, but all on all this is quite a painful
situation for older OSes (where older in principle means older than
10.9 or 10.7, even though compilation on 10.7 is also horribly broken
on itself). Yes, gcc would be an alternative to build CMake which does
not depend on CMake itself, but then we end up mixing different
stdlibs and Apple is avoiding GPL 3 like a plague (packages for
llvm/clang are maintained by an Apple employee).

Mojca