MachO: actually set linker-private prefix at MC level.

This was accidentally omitted from r205081.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205083 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCAsmInfoDarwin.cpp

@@ -23,6 +23,7 @@ void MCAsmInfoDarwin::anchor() { }
 MCAsmInfoDarwin::MCAsmInfoDarwin() {
   // Common settings for all Darwin targets.
   // Syntax:
+  LinkerPrivateGlobalPrefix = "l";
   HasSingleParameterDotFile = false;
   HasSubsectionsViaSymbols = true;