[roll] Roll third_party/platforms Add aix os constraint. (#126)

Believe it or not, I may have to build for AIX with Bazel in the foreseable future.
Having this here makes it possible to upstream that case into select() clauses
of legacy C code that has made its way into the BCR.
Original-Revision: cdcb20772abb890385de6e4ed3ea650b042ebe45

Roller-URL: https://cr-buildbucket.appspot.com/build/8702721779204358209
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I8ec58263b1e130175d453d08c89ac9b2d6f96c68
Reviewed-on: https://fuchsia-review.googlesource.com/c/boards/emac/+/1377208
Commit-Queue: GI Roller <global-integration-roller@fuchsia-infra.iam.gserviceaccount.com>