don't use @_implementationOnly

Author: lhoward

Sources/Supporting/Locking.swift

@@ -10,13 +10,13 @@
 //===----------------------------------------------------------------------===//
 
 #if canImport(Darwin)
-@_implementationOnly import Darwin
+import Darwin
 #elseif canImport(Glibc)
-@_implementationOnly import Glibc
+import Glibc
 #elseif canImport(WinSDK)
-@_implementationOnly import WinSDK
+import WinSDK
 #elseif canImport(Android)
-@_implementationOnly import Android
+import Android
 #endif
 
 internal struct Lock {