MC: Change MCAsmBackend::writeNopData() to take a raw_ostream instead of an MCObjectWriter. NFCI.

To make this work I needed to add an endianness field to MCAsmBackend
so that writeNopData() implementations know which endianness to use.

Part of PR37466.

Differential Revision: https://reviews.llvm.org/D47035

llvm-svn: 332857
diff --git a/llvm/lib/MC/MCAsmBackend.cpp b/llvm/lib/MC/MCAsmBackend.cpp
index d675a98..8406d23 100644
--- a/llvm/lib/MC/MCAsmBackend.cpp
+++ b/llvm/lib/MC/MCAsmBackend.cpp
@@ -18,10 +18,8 @@
 
 using namespace llvm;
 
-MCAsmBackend::MCAsmBackend() : CodePadder(new MCCodePadder()) {}
-
-MCAsmBackend::MCAsmBackend(std::unique_ptr<MCCodePadder> TargetCodePadder)
-    : CodePadder(std::move(TargetCodePadder)) {}
+MCAsmBackend::MCAsmBackend(support::endianness Endian)
+    : CodePadder(new MCCodePadder()), Endian(Endian) {}
 
 MCAsmBackend::~MCAsmBackend() = default;