Updated deps
Platform configuration

FIXME: avoid using Xcode build and switch to a patched libuv
Runtime support for arm on iOS
Disable generating split-stack code

Allows to compile for archs which do not have (or have limited)
segmented stack support like embedded.
Basic iOS support
Better dylib skipping based on Alex Crichton code
Cosmetic fixes & comments
There should be no metadata to read on iOS
Updated compiler-rt

Previous update unfortunately included changes which
broke Android compilation. This update fixes it and
should allow correct compilation of SjLj for iOS and
all builtins for Android.
auto merge of #14715 : vhbit/rust/ios-pr2, r=alexcrichton