PR d/90064
libphobos: Merge upstream phobos 428460ddd
Defines growDownwards on SPARC64, initial patch by Rainer Orth.
Backports another fix to std.process, allowing permissions tests to be
skipped when running as root.
Reviewed-on: https://github.com/dlang/phobos/pull/6962
From-SVN: r270483
