Fix the build of the Swift Package with Xcode 12.5 beta 1

[layoutSubviews]

What does this PR do?

Fix a build failure with the newly released Xcode 12.5 beta 1

Where should the reviewer start?

Try to build the Swift Package with Xcode 12.5 beta 1

How should this be manually tested?

Build.

Any background context you want to provide?

Xcode 12.5 beta 1 was released today, and introduces a new error when a #if statement is used with an undefined variable: "error: 'TARGET_OS_IPHONE' is not defined, evaluates to 0". This affects a single file, SEGIntegrationsManager.m.

Questions:

• Does the docs need an update?
  No.
• Are there any security concerns?
  No.
• Do we need to update engineering / success?
  No.

[bsneed]

thanks @layoutSubviews !