NVPTXTargetObjectFile.h: Initialize some pointers as NULL in the constructor of NVPTXTargetObjectFile. ~NVPTXTargetObjectFile() tries to delete them.

It caused crash on some hosts since r184595.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184728 91177308-0d34-0410-b5e6-96231b3b80d8
llvm/test/DebugInfo/arguments.ll: Add explicit -mtriple=x86_64-unknown-unknown.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184729 91177308-0d34-0410-b5e6-96231b3b80d8
llvm/test/CodeGen/X86/legalize-shift-64.ll: Add explicit -mtriple=i686-unknown-unknown.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184730 91177308-0d34-0410-b5e6-96231b3b80d8
llvm/test/CodeGen/X86: Add explicit -mtriple=x86_64-unknown-unknown.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184731 91177308-0d34-0410-b5e6-96231b3b80d8
Look for Python 2 before Python 3 in CMakeLists.txt

All of LLVM's Python scripts only support Python 2 for widely understood
reasons.

Patch by Yonggang Luo.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184732 91177308-0d34-0410-b5e6-96231b3b80d8