Switch Powerpc64 Big Endian to ELFv2 on OpenBSD.

Index: lib/Target/PowerPC/PPCTargetMachine.cpp
--- lib/Target/PowerPC/PPCTargetMachine.cpp.orig
+++ lib/Target/PowerPC/PPCTargetMachine.cpp
@@ -228,6 +228,8 @@ static PPCTargetMachine::PPCABI computeTargetABI(const
   case Triple::ppc64le:
     return PPCTargetMachine::PPC_ABI_ELFv2;
   case Triple::ppc64:
+    if (TT.isOSOpenBSD())
+      return PPCTargetMachine::PPC_ABI_ELFv2;
     return PPCTargetMachine::PPC_ABI_ELFv1;
   default:
     return PPCTargetMachine::PPC_ABI_UNKNOWN;