[llvm] [BOLT][Hexagon] Add Hexagon MCPlusBuilder, relocations (PR #192189)

[Brian Cain via llvm-commits]

androm3da wrote:

> > I need to take a closer look at parts shared with other backends.
> 
> I have decomposed `[BOLT] Add generic VLIW bundle emission infrastructure` into its own commit for easier reviewing and if desired I can land this in its own PR.

@maksfb I have put that commit into its own PR at #200916

There's a couple of small changes remaining in this PR in architecture-independent code which could be broken out to their own PR if desired:

- [ ] COUNT_NO_PROFILE assert -> treat as zero: fixes a latent crash for any target without profile data
- [ ] Skip-call fix: calls can't be relaxed via intra-function trampolines on any target
- [ ] Replace `BitsAvailable == LongestJumpBits` with `BitsAvailable >= getUncondBranchEncodingSize()`

https://github.com/llvm/llvm-project/pull/192189