MC: Separate creating a generic object writer from creating a target object writer. NFCI.

With this we gain a little flexibility in how the generic object
writer is created.

Part of PR37466.

Differential Revision: https://reviews.llvm.org/D47045

llvm-svn: 332868
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
index 3cd52fe..dfa3390 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
@@ -236,9 +236,7 @@
   }
 }
 
-std::unique_ptr<MCObjectWriter>
-llvm::createARMELFObjectWriter(raw_pwrite_stream &OS, uint8_t OSABI,
-                               bool IsLittleEndian) {
-  return createELFObjectWriter(llvm::make_unique<ARMELFObjectWriter>(OSABI), OS,
-                               IsLittleEndian);
+std::unique_ptr<MCObjectTargetWriter>
+llvm::createARMELFObjectWriter(uint8_t OSABI) {
+  return llvm::make_unique<ARMELFObjectWriter>(OSABI);
 }