Fix ARM unwinding.
auto merge of #11301 : vadimcn/rust/fix-android, r=brson

This fixes stack unwinding on targets using ARM EHABI.
closes #11147
Don't allow single-variant enums to be dereferenced. #6246

I'm not sure if this was even intentional at this point.
Don't allow newtype structs to be dereferenced. #6246
rustc: Add error about obsolete struct deref
doc: Fix tutorial for struct deref
doc: Fix an inexplicable error in a tutorial example

This code was wrong but apparently worked before removing struct
deref. I don't know why.