[stdlib] alter inconsistent declarations

`private` declarations should never be allowed to carry the `@_alwaysEmitIntoClient` attribute. This has been allowed by mistake for a while, but newer compilers should make this an error.

Author: glessard

stdlib/public/core/CString.swift

@@ -77,7 +77,7 @@ extension String {
   }
 
   @_alwaysEmitIntoClient
-  private init(_checkingCString bytes: UnsafeBufferPointer<UInt8>) {
+  internal init(_checkingCString bytes: UnsafeBufferPointer<UInt8>) {
     guard let length = bytes.firstIndex(of: 0) else {
       _preconditionFailure(
         "input of String.init(cString:) must be null-terminated"

stdlib/public/core/String.swift

@@ -428,7 +428,7 @@ extension String {
   // check in String(decoding:as:).
   @_alwaysEmitIntoClient
   @inline(never) // slow-path
-  private static func _fromNonContiguousUnsafeBitcastUTF8Repairing<
+  internal static func _fromNonContiguousUnsafeBitcastUTF8Repairing<
     C: Collection
   >(_ input: C) -> (result: String, repairsMade: Bool) {
     _internalInvariant(C.Element.self == UInt8.self)