[SE-0331] Mark unsafe pointer conformances to Sendable as explicitly unavailable

This is a preferred way to make sure that Sendable inference doesn't
happen for these types because they are marked as @Frozen.

(cherry picked from commit a0dfab9)

Author: xedin

stdlib/public/core/BridgeObjectiveC.swift

@@ -589,7 +589,8 @@ extension UnsafeRawPointer {
   }
 }
 
-extension AutoreleasingUnsafeMutablePointer { }
+@available(*, unavailable)
+extension AutoreleasingUnsafeMutablePointer: Sendable { }
 
 internal struct _CocoaFastEnumerationStackBuf {
   // Clang uses 16 pointers.  So do we.

stdlib/public/core/CTypes.swift

@@ -207,6 +207,9 @@ extension OpaquePointer: Hashable {
   }
 }
 
+@available(*, unavailable)
+extension OpaquePointer : Sendable { }
+
 extension OpaquePointer: CustomDebugStringConvertible {
   /// A textual representation of the pointer, suitable for debugging.
   public var debugDescription: String {
@@ -297,6 +300,9 @@ extension CVaListPointer: CustomDebugStringConvertible {
 
 #endif
 
+@available(*, unavailable)
+extension CVaListPointer: Sendable { }
+
 /// Copy `size` bytes of memory from `src` into `dest`.
 ///
 /// The memory regions `src..<src + size` and

stdlib/public/core/UnsafeBufferPointer.swift.gyb

@@ -1197,8 +1197,14 @@ extension Unsafe${Mutable}BufferPointer: CustomDebugStringConvertible {
       + "(start: \(_position.map(String.init(describing:)) ?? "nil"), count: \(count))"
   }
 }
+
+@available(*, unavailable)
+extension Unsafe${Mutable}BufferPointer: Sendable { }
 %end
 
+@available(*, unavailable)
+extension UnsafeBufferPointer.Iterator: Sendable { }
+
 
 // ${'Local Variables'}:
 // eval: (read-only-mode 1)

stdlib/public/core/UnsafePointer.swift

@@ -1172,3 +1172,8 @@ public struct UnsafeMutablePointer<Pointee>: _Pointer {
     )._unsafelyUnwrappedUnchecked
   }
 }
+
+@available(*, unavailable)
+extension UnsafePointer: Sendable { }
+@available(*, unavailable)
+extension UnsafeMutablePointer: Sendable { }

stdlib/public/core/UnsafeRawBufferPointer.swift.gyb

@@ -1303,6 +1303,14 @@ public func _withUnprotectedUnsafeBytes<T, Result>(
   return try body(buffer)
 }
 
+@available(*, unavailable)
+extension UnsafeRawBufferPointer: Sendable { }
+@available(*, unavailable)
+extension UnsafeRawBufferPointer.Iterator: Sendable { }
+@available(*, unavailable)
+extension UnsafeMutableRawBufferPointer: Sendable { }
+
+
 // ${'Local Variables'}:
 // eval: (read-only-mode 1)
 // End:

stdlib/public/core/UnsafeRawPointer.swift

@@ -1486,3 +1486,8 @@ extension OpaquePointer {
     self._rawValue = unwrapped._rawValue
   }
 }
+
+@available(*, unavailable)
+extension UnsafeRawPointer: Sendable { }
+@available(*, unavailable)
+extension UnsafeMutableRawPointer: Sendable { }