Allow repeated registration again.

Our use of -fvisibility-inlines-hidden means we cannot check function pointers
against non null values.

Unfortunately, we also cannot assert that the callbacks are initialized only
once. The problem is that lldb has multiple subsystems that need to call this
and they don't have a unique initialization order.

Thanks to Sean Callanan for reporting it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192835 91177308-0d34-0410-b5e6-96231b3b80d8
DIEHash: Include the trailing zero byte after the children of a DIE

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192836 91177308-0d34-0410-b5e6-96231b3b80d8
Add support for the VSX target attribute. No functional change
as we don't actually use it to emit any code yet.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192837 91177308-0d34-0410-b5e6-96231b3b80d8
Remove ambiguity introduced in r192836

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192840 91177308-0d34-0410-b5e6-96231b3b80d8