Add devel/cloudabi-cloudlibc.

[ed]

Summary

CloudABI uses a C library called cloudlibc. It's similar to a standard UNIX C library, except that all features that use global namespaces have been removed. The advantage is that this causes compiler errors when trying to use existing software, instead of causing it to fail in unpredictable ways at runtime.

This package installs a copy of cloudlibc for CloudABI/x86-64 (the only supported platform for now). It is installed in the right place, so that Clang and Binutils can find the headers/library archives.

Test Plan

The annoying thing is that the compiler, binutils and this port alone are still not sufficient to compile working binaries, for the reason that we still need to add compiler-rt. I will work on this after cloudabi-clang and this port land.