[Offload] Fix not copying the buffer identifier of offloading files

Summary:
This caused an error when copying a file of the same name when multiple
architectures needed the file. The buffer identifier which we use for
the name in `-save-temps` mode would be empty and create in invalid
filename. Copy this correctly now.

Author: jhuber6

llvm/include/llvm/Object/OffloadBinary.h

@@ -165,7 +165,8 @@ class OffloadFile : public OwningBinary<OffloadBinary> {
   /// Make a deep copy of this offloading file.
   OffloadFile copy() const {
     std::unique_ptr<MemoryBuffer> Buffer = MemoryBuffer::getMemBufferCopy(
-        getBinary()->getMemoryBufferRef().getBuffer());
+        getBinary()->getMemoryBufferRef().getBuffer(),
+        getBinary()->getMemoryBufferRef().getBufferIdentifier());
 
     // This parsing should never fail because it has already been parsed.
     auto NewBinaryOrErr = OffloadBinary::create(*Buffer);