[stdlib] Initial FreeBSD port.

[dcci]

Initial FreeBSD port of stdlib/FreeBSDlibc.
Thanks!

Davide

[gribozavr]

Any reason to not do an 'or' and add this to the previous 'if' statement? I expect these three libraries to be buildable on any unix-y system.

[gribozavr]

@dcci Thank you for your patch!

I don't like the duplication of the overlay code. Is there a way you can think of we could share the code between FreeBSD and Linux, and, potentially, Darwin?

[gribozavr]

There is also TestRunPredicate below that should be updated, and then you should be able to write a test like this validation-test/stdlib/StdlibUnittestLinux.swift but for FreeBSD.

[dcci]

I see, thanks!

[dcci]

The main difference is the module map and __environ. There's probably a way to make more code to be shared, I'll think about it harder between today and tomorrow and submit a new patch

Thanks for your review!

Davide

[gribozavr]

@dcci Thanks! I would be much happier with more complex CMake code than duplication of actual overlay code.