Use raw_pwrite_stream in the object writer/streamer.

The ELF object writer will take advantage of that in the next commit.

llvm-svn: 234950
diff --git a/llvm/lib/MC/MCELFStreamer.cpp b/llvm/lib/MC/MCELFStreamer.cpp
index 8f0691b..aa05390 100644
--- a/llvm/lib/MC/MCELFStreamer.cpp
+++ b/llvm/lib/MC/MCELFStreamer.cpp
@@ -647,7 +647,7 @@
 }
 
 MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
-                                    raw_ostream &OS, MCCodeEmitter *CE,
+                                    raw_pwrite_stream &OS, MCCodeEmitter *CE,
                                     bool RelaxAll) {
   MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
   if (RelaxAll)