Rollup of 7 pull requests#68942

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Dylan-DPC-zz wants to merge 19 commits intorust-lang:masterfrom

Dylan-DPC-zz:rollup-ylouifu

Commits on Feb 1, 2020

Remove some unsound specializations
matthewjasper
committed

Commits on Feb 3, 2020

rustc_codegen_ssa: don't treat inlined variables as debuginfo arguments.
eddyb
committed

Commits on Feb 4, 2020

Fix and test implementation of BTreeMap's first_entry, last_entry, pop_first, pop_last
ssomers
committed

Commits on Feb 5, 2020

Reorder declarations of Result::export/unwrap to match Option
brson
committed
Reorder declarations of Result::expect_err/unwrap_err to match Option
brson
committed

Commits on Feb 6, 2020

rustc_codegen_llvm: always set AlwaysPreserve on all debuginfo variables.
eddyb
committed

Commits on Feb 8, 2020