Revert Implement sys::fs::copy_file using the macOS copyfile(3) API to support APFS clones.

This reverts r358628 (git commit 91a06bee788262a294527b815354f380d99dfa9b)
while investigating a crash reproducer bot failure.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358634 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Path.cpp

@@ -935,7 +935,6 @@ std::error_code create_directories(const Twine &Path, bool IgnoreExisting,
   return create_directory(P, IgnoreExisting, Perms);
 }
 
-#ifndef __APPLE__
 static std::error_code copy_file_internal(int ReadFD, int WriteFD) {
   const size_t BufSize = 4096;
   char *Buf = new char[BufSize];
@@ -989,7 +988,6 @@ std::error_code copy_file(const Twine &From, int ToFD) {
 
   return EC;
 }
-#endif
 
 ErrorOr<MD5::MD5Result> md5_contents(int FD) {
   MD5 Hash;