OSAtomic* deprecation

[dlewanda]

Short description of the issue:
With the final release of Xcode 10 and watchOS 5, Apple is rejecting submission of watchOS applications with a WATCHOS_DEPLOYMENT_TARGET below 3.0

Expected outcome:

Apple accepts the application via upload through the normal means.

What actually happens:

The application upload is rejected with the following message:

[02:22:23]: [iTMSTransporter] [2018-09-25 02:22:23 MDT] <main> ERROR: ERROR ITMS-90081: "This bundle is invalid. Applications built for more than one architecture require an iOS Deployment Target of 3.0 or later."

While the error message suggests the iOS Deployment target is wrong, it appears this is a misnomer, as our iOS deployment target is 9.0. Others are seeing this issue as well:
https://forums.developer.apple.com/thread/108853

We did have to update the watchOS deployment target from 2.0 (the default) on other frameworks we use. We had been relying on the precompiled version of RxSwift to expedite our build times, but it appears that the current minimum version compiled in is 2.0 as shown here:
https://github.com/ReactiveX/RxSwift/blob/master/Rx.xcodeproj/project.pbxproj#L6428

Self contained code example that reproduces the issue:

The issue isn't specific to any code, but how it's built via the project setting linked above

RxSwift/RxCocoa/RxBlocking/RxTest version/commit
https://github.com/ReactiveX/RxSwift/releases/tag/4.3.1

Platform/Environment

• iOS
• macOS
• tvOS
• watchOS
• playgrounds

How easy is to reproduce? (chances of successful reproduce after running the self contained code)

• easy, 100% repro
• sometimes, 10%-100%
• hard, 2% - 10%
• extremely hard, %0 - 2%

Xcode version:

  10.0 (10A255)

⚠️ Fields below are optional for general issues or in case those questions aren't related to your issue, but filling them out will increase the chances of getting your issue resolved. ⚠️

Installation method:

• CocoaPods
• Carthage
• Git submodules

I have multiple versions of Xcode installed:
(so we can know if this is a potential cause of your issue)

• yes (which ones: 9.0, 9.1, 9.2, 9.3.1, 10.0)
• no

Level of RxSwift knowledge:
(this is so we can understand your level of knowledge
and formulate the response in an appropriate manner)

• just starting
• I have a small code base
• I have a significant code base

[dlewanda]

Hi @freak4pc, given your involvement in #1737, I was wondering if you might have some insight here. I'm trying to figure out how to get #1753 to not use the warnings that are being treated as errors in the CI process, but I'm not having much luck there.

[MikeDyna]

Any news on when this is gonna be merged?

[freak4pc]

This isn't a PR so there's nothing to merge 😛
Unfortunately this deprecation warning is a bit of an issue but as far as I'm concerned, we should leave the warnings as-is, as there's really no way around it. I'm not entirely sure where the warnings are raised to "error level", but would gladly look at a PR that disables that.

[dlewanda]

I started on a PR in #1753 but have been pulled away by other commitments. I hope to get back to it very soon and get it passing CI by silencing the deprecation warnings