MC: Add TargetAsmBackend::WriteNopData and use to eliminate some target dependencies in MCMachOStreamer and MCAssembler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99248 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCMachOStreamer.cpp b/lib/MC/MCMachOStreamer.cpp
index 51a2d45..a52d962 100644
--- a/lib/MC/MCMachOStreamer.cpp
+++ b/lib/MC/MCMachOStreamer.cpp
@@ -353,8 +353,7 @@
                                         unsigned MaxBytesToEmit) {
   if (MaxBytesToEmit == 0)
     MaxBytesToEmit = ByteAlignment;
-  // FIXME: The 0x90 is the default x86 1 byte nop opcode.
-  new MCAlignFragment(ByteAlignment, 0x90, 1, MaxBytesToEmit,
+  new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
                       true /* EmitNops */, CurSectionData);
 
   // Update the maximum alignment on the current section if necessary.