NFC: Move API uses of MD5::MD5Result to Optional rather than a pointer.

Differential Revision: https://reviews.llvm.org/D60290

llvm-svn: 357736
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
index 427de49..f19f6d0 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
@@ -296,7 +296,7 @@
 
   /// If the \p File has an MD5 checksum, return it as an MD5Result
   /// allocated in the MCContext.
-  MD5::MD5Result *getMD5AsBytes(const DIFile *File) const;
+  Optional<MD5::MD5Result> getMD5AsBytes(const DIFile *File) const;
 
 protected:
   ~DwarfUnit();