Remove the legacy Xcode 16 entry point function on non-Darwin platforms. (#545)

This PR removes `swt_copyABIEntryPoint_v0()`, which is an older version
of the approved `swt_abiv0_getEntryPoint()` entry point function used by
Xcode 16 Beta 1 but not used on non-Darwin platforms.

The symbol remains available on Darwin for the benefit of Xcode 16 beta
users. It will be removed from the Darwin builds in a future update.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/Testing/ABI/EntryPoints/ABIEntryPoint.swift

@@ -65,6 +65,7 @@ extension ABIv0 {
   unsafeBitCast(ABIv0.entryPoint, to: UnsafeRawPointer.self)
 }
 
+#if !SWT_NO_SNAPSHOT_TYPES
 // MARK: - Xcode 16 Beta 1 compatibility
 
 /// An older signature for ``ABIv0/EntryPoint-swift.typealias`` used by Xcode 16
@@ -94,6 +95,9 @@ typealias ABIEntryPoint_v0 = @Sendable (
   }
   return .init(result)
 }
+#endif
+
+// MARK: -
 
 /// A common implementation for ``ABIv0/entryPoint-swift.type.property`` and
 /// ``copyABIEntryPoint_v0()`` that provides Xcode 16 Beta 1 compatibility.
@@ -120,6 +124,8 @@ private func entryPoint(
   let exitCode = await entryPoint(passing: args, eventHandler: eventHandler)
 
   // To maintain compatibility with Xcode 16 Beta 1, suppress custom exit codes.
+  // (This is also needed by ABIv0.entryPoint to correctly treat the no-tests as
+  // a successful run.)
   if exitCode == EXIT_NO_TESTS_FOUND {
     return EXIT_SUCCESS
   }

Tests/TestingTests/ABIEntryPointTests.swift

@@ -19,6 +19,7 @@ private import _TestingInternals
 
 @Suite("ABI entry point tests")
 struct ABIEntryPointTests {
+#if !SWT_NO_SNAPSHOT_TYPES
   @available(*, deprecated)
   @Test func v0_experimental() async throws {
     var arguments = __CommandLineArguments_v0()
@@ -52,18 +53,12 @@ struct ABIEntryPointTests {
     passing arguments: __CommandLineArguments_v0,
     recordHandler: @escaping @Sendable (_ recordJSON: UnsafeRawBufferPointer) -> Void = { _ in }
   ) async throws -> CInt {
-#if !os(Linux) && !SWT_NO_DYNAMIC_LINKING
     // Get the ABI entry point by dynamically looking it up at runtime.
-    //
-    // NOTE: The standard Linux linker does not allow exporting symbols from
-    // executables, so dlsym() does not let us find this function on that
-    // platform when built as an executable rather than a dynamic library.
     let copyABIEntryPoint_v0 = try #require(
       symbol(named: "swt_copyABIEntryPoint_v0").map {
         unsafeBitCast($0, to: (@convention(c) () -> UnsafeMutableRawPointer).self)
       }
     )
-#endif
     let abiEntryPoint = copyABIEntryPoint_v0().assumingMemoryBound(to: ABIEntryPoint_v0.self)
     defer {
       abiEntryPoint.deinitialize(count: 1)
@@ -82,6 +77,7 @@ struct ABIEntryPointTests {
     // Call the entry point function.
     return try await abiEntryPoint.pointee(.init(argumentsJSON), recordHandler)
   }
+#endif
 
   @Test func v0() async throws {
     var arguments = __CommandLineArguments_v0()