Don't loop unswitch vector selects

Otherwise we could produce `br <2x i1>` which are of course not legal.

```
Branch condition is not 'i1' type!
  br <2 x i1> %cond.fr1, label %entry.split.us, label %entry.split
  %cond.fr1 = freeze <2 x i1> %cond
LLVM ERROR: Broken module found, compilation aborted!
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: /home/vchuravy/builds/llvm/bin/opt -passes=simple-loop-unswitch<nontrivial> -S
```

Fixes https://reviews.llvm.org/D138526

Differential Revision: https://reviews.llvm.org/D149560

Author: vchuravy

llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

@@ -2810,7 +2810,8 @@ static bool unswitchBestCondition(
     for (auto &I : *BB) {
       if (auto *SI = dyn_cast<SelectInst>(&I)) {
         auto *Cond = SI->getCondition();
-        if (!isa<Constant>(Cond) && L.isLoopInvariant(Cond))
+        // restrict to simple boolean selects
+        if (!isa<Constant>(Cond) && L.isLoopInvariant(Cond) && Cond->getType()->isIntegerTy(1))
           UnswitchCandidates.push_back({&I, {Cond}});
       } else if (CollectGuards && isGuard(&I)) {
         auto *Cond =