Revert using fcopyfile(3) to implement sys::fs::copy_file(Twine, int) on macOS

It turns out that I mesread the man page and fcopyfile(3) does not
actually support COPYFILE_CLONE for files.

<rdar://problem/50148757>

llvm-svn: 359127
diff --git a/llvm/lib/Support/Path.cpp b/llvm/lib/Support/Path.cpp
index 9466591..d60c135 100644
--- a/llvm/lib/Support/Path.cpp
+++ b/llvm/lib/Support/Path.cpp
@@ -935,7 +935,6 @@
   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];
@@ -960,6 +959,7 @@
   return std::error_code();
 }
 
+#ifndef __APPLE__
 std::error_code copy_file(const Twine &From, const Twine &To) {
   int ReadFD, WriteFD;
   if (std::error_code EC = openFileForRead(From, ReadFD, OF_None))
@@ -977,6 +977,7 @@
 
   return EC;
 }
+#endif
 
 std::error_code copy_file(const Twine &From, int ToFD) {
   int ReadFD;
@@ -989,7 +990,6 @@
 
   return EC;
 }
-#endif
 
 ErrorOr<MD5::MD5Result> md5_contents(int FD) {
   MD5 Hash;