Building libuv with Xcode for iOS

A little bit cumbersome but for now much easier to configure than
Makefile based
WIP: TLS support for iOS target

Goal is to get _tlv_initializer() and _tlv_get_addr() from dyld source
to be available in runtime.

There is a work of Dan Olson who patched LLVM to support TLS code
generation for iOS using those functions