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/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
index 3e98ba3..61649c4 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
@@ -413,7 +413,7 @@
   Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
 }
 
-MCObjectWriter *llvm::createAArch64MachObjectWriter(raw_ostream &OS,
+MCObjectWriter *llvm::createAArch64MachObjectWriter(raw_pwrite_stream &OS,
                                                     uint32_t CPUType,
                                                     uint32_t CPUSubtype) {
   return createMachObjectWriter(