Revert "Improve memory ownership/management in TableGen by unique_ptrifying TreePattern's Tree member."

This reverts commit r222183.

Broke on the MSVC buildbots due to MSVC not producing default move
operations - I'd fix it immediately but just broke my build system a
bit, so backing out until I have a chance to get everything going again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222187 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "ADT: correctly report isMSVCEnvironment for windows itanium"

This reverts commit r222180.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222188 91177308-0d34-0410-b5e6-96231b3b80d8
IR: Simplify uniquing for MDNode

Change uniquing from a `FoldingSet` to a `DenseSet` with custom
`DenseMapInfo`.  Unfortunately, this doesn't save any memory, since
`DenseSet<T>` is a simple wrapper for `DenseMap<T, char>`, but I'll come
back to fix that later.

I used the name `GenericDenseMapInfo` to the custom `DenseMapInfo` since
I'll be splitting `MDNode` into two classes soon: `MDNodeFwdDecl` for
temporaries, and `GenericMDNode` for everything else.

I also added a non-debug-info reduced version of a type-uniquing test
that started failing on an earlier draft of this patch.

Part of PR21532.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222191 91177308-0d34-0410-b5e6-96231b3b80d8
Debug Info: In DIBuilder, the context field of a global variable is updated to
use DIScopeRef.

A paired commit at clang will follow to show cases where we will use an
identifer for the context of a global variable.

rdar://18958417


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222195 91177308-0d34-0410-b5e6-96231b3b80d8
Revert r222040 because of bot failure.

http://lab.llvm.org:8080/green/job/clang-Rlto_master/298/
Hopefully, bot will be green.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222203 91177308-0d34-0410-b5e6-96231b3b80d8
IR: Split MDNode into GenericMDNode and MDNodeFwdDecl

Split `MDNode` into two classes:

  - `GenericMDNode`, which is uniquable (and for now, always starts
    uniqued).  Once `Metadata` is split from the `Value` hierarchy, this
    class will lose the ability to RAUW itself.

  - `MDNodeFwdDecl`, which is used for the "temporary" interface, is
    never uniqued, and isn't managed by `LLVMContext` at all.

I've left most of the guts in `MDNode` for now, but I'll incrementally
move things to the right places (or delete the functionality, as
appropriate).

Part of PR21532.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222205 91177308-0d34-0410-b5e6-96231b3b80d8
Support ELF files of unknown type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222208 91177308-0d34-0410-b5e6-96231b3b80d8
Fix covered switch warning

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222209 91177308-0d34-0410-b5e6-96231b3b80d8
BPF backend

work in progress
will be rebased

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>