The dominator tree gained an optimization to use block numbers instead
of a DenseMap to store blocks. Given that machine basic blocks already
have numbers, expose these via appropriate GraphTraits. For debugging,
block number epochs are added to MachineFunction -- this greatly helps
in finding uses of block numbers after RenumberBlocks().

In a few cases where dominator trees are preserved across renumberings,
the dominator tree is updated to use the new numbers.

- Add `MachineLoopAnalysis`.
- Add `MachineLoopPrinterPass`.
- Convert to `MachineLoopInfoWrapperPass` in legacy pass manager.

Prepare for new pass manager version of `MachineDominatorTreeAnalysis`.
We may need a machine dominator tree version of `DomTreeUpdater` to
handle `SplitCriticalEdge` in some CodeGen passes.

In the WebAssembly back end, the TrapUnreachable option is currently
load-bearing for correctness, inserting wasm `unreachable` instructions
where needed to create valid wasm. There is another option,
NoTrapAfterNoreturn, that removes some of those traps and causes
incorrect wasm to be emitted.

This turns off `NoTrapAfterNoreturn` for the Wasm backend and adds new   
tests.

Move WebAssemblyUtilities from Utils to the CodeGen library. It
primarily deals in MIR layer types, so it really lives in the CodeGen
library.

Move a variety of other things around to try create better separation.

See issue #64166 for more info on layering.

Move llvm/include/CodeGen/WasmAddressSpaces.h back to
llvm/lib/Target/WebAssembly/Utils.

Differential Revision: https://reviews.llvm.org/D156472

Without explicitly checking and erroring out, an invalid personality
function, which is not `__gxx_wasm_personality_v0`, caused
a segmentation fault down the line because `WasmEHFuncInfo` was not
created. This explicitly checks the validity of personality functions in
functions with EH pads and errors out explicitly with a helpful error
message. This also adds some more assertions to ensure `WasmEHFuncInfo`
is correctly created and non-null.

Invalid personality functions wouldn't be generated by our Clang, but
can be present in handwritten ll files, and more often, in files
transformed by passes like `metarenamer`, which is often used with
`bugpoint` to simplify names in `bugpoint`-reduced files.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D152203

Use isPhysical/isVirtual methods.

With C++17 there is no Clang pedantic warning or MSVC C5051.

Previously WebAssemblyCFGStackify, WebAssemblyInstrInfo, and
WebAssemblyPeephole all had equivalent logic for this. Move it into a
common helper in WebAssemblyUtilities.