Support macCatalyst

[pokryfka]

AsyncHTTPClient 1.2.1 commit hash: 4b4d660

Context:
Building AsyncHTTPClient for Mac Catalyst fails with errors:

'sec_protocol_options_set_tls_min_version' is unavailable in Mac Catalyst
'sec_protocol_options_set_tls_max_version' is unavailable in Mac Catalyst

Steps to reproduce:

1. Open Package.swift in Xcode
2. Select platform My Mac (Mac Catalyst)
3. Build

$ swift --version
Apple Swift version 5.2.4 (swiftlang-1103.0.32.9 clang-1103.0.32.53)
Target: x86_64-apple-darwin19.6.0

Operating system: macOS Catalina 10.15.6

$ uname -a
Darwin xxx 19.6.0 Darwin Kernel Version 19.6.0: Thu Jun 18 20:49:00 PDT 2020; root:xnu-6153.141.1~1/RELEASE_X86_64 x86_64

Xcode 11.6
Mac Catalyst 13.0

[Lukasa]

Yes, I think the availability guards in TLSConfiguration need to be updated to cover macCatalyst. Are you interested in doing that?

[pokryfka]

@Lukasa

I could fix the compilation.

However I think ideally this should be accompanied with CI build tests on different platforms (iOS, macCatalyst, ...) which I dont think I could create/update on my own.

My understanding is, please correct me if I am wrong, that while the main target of AsyncHTTPClient is Linux
other platforms, including macOS and iOS with its "derivatives", are also supported and as such it would be nice to test, at the very least, compilation.

[Lukasa]

There are some logistical difficulties with that in general that @tomerd will need to do some thinking about. Suffice it to say that while we agree these should be tested, for now I think it's mostly important to get the software building again.