Revert "Migrate from UnsafePointer<Void> to UnsafeRawPointer. (#3724)"

This reverts commit ece0951924.

This results in lldb failues on linux that I can't readily debug.
Backing out until they can be resolved.

test/Interpreter/SDK/c_pointers.swift

@@ -128,7 +128,7 @@ puts(s)
 
 var unsorted = [3, 14, 15, 9, 2, 6, 5]
 qsort(&unsorted, unsorted.count, sizeofValue(unsorted[0])) { a, b in
-  return Int32(a!.load(as: Int.self) - b!.load(as: Int.self))
+  return Int32(UnsafePointer<Int>(a!).pointee - UnsafePointer<Int>(b!).pointee)
 }
 // CHECK-NEXT: [2, 3, 5, 6, 9, 14, 15]
 print(unsorted)