SwiftPM package always produces warnings when `import libzstd`

[yyaroshevich]

Describe the bug Import libzstd into Swift file causes compilation warnings.

To Reproduce Steps to reproduce the behavior:

1. Clone repro repository git clone https://github.com/yyaroshevich/zstd-warning-swift.git
2. Compile project (cd zstd-warning-swift; xcodebuild -project ./ZStdWarning.xcodeproj)
3. Observe compilation is failed due to warnings (warnings as errors are enabled)

Expected behavior No warnings produced when import libzstd.

Screenshots and charts

Desktop (please complete the following information):

• OS: Mac OS X 13.0.1
• Version libzstd: dev branch & 1.5.2
• Compiler: Swift 5.7, XCode 14.1