[MCJIT][test] Move remaining MCJIT interpreter tests to Interpreter/ subdirectory

[asb]

I left these alone in #124463 but I think it makes sense to clean these up as well (which Philip also noted in #124464).

---

This should be a trivial change, the only reason I held off was wanting to check whether there are any concerns about the tests in the Interpreter/ directory being gated on config.enable_ffi. Some, but not all of the tests being moved contain foreign calls. It seems reasonable to me (even if it's possible a small number of tests could run but don't in some configurations).

[github-actions]

⚠️ undef deprecator found issues in your code. ⚠️

You can test this locally with the following command:

git diff -U0 --pickaxe-regex -S '([^a-zA-Z0-9#_-]undef[^a-zA-Z0-9_-]|UndefValue::get)' 606cf887416ba2f136f3104ac12469fc81f73968 c9555cfa503fae0828d9b5a3e3bc803d2d840160 llvm/test/ExecutionEngine/Interpreter/2010-01-15-UndefValue.ll llvm/test/ExecutionEngine/Interpreter/test-interp-target-ext-type.ll llvm/test/ExecutionEngine/Interpreter/test-interp-vec-cast.ll llvm/test/ExecutionEngine/Interpreter/test-interp-vec-insertelement.ll llvm/test/ExecutionEngine/Interpreter/test-interp-vec-insertextractvalue.ll llvm/test/ExecutionEngine/Interpreter/test-interp-vec-loadstore.ll llvm/test/ExecutionEngine/Interpreter/test-interp-vec-select.ll llvm/test/ExecutionEngine/Interpreter/test-interp-vec-shift.ll llvm/test/ExecutionEngine/Interpreter/test-interp-vec-shuffle.ll

The following files introduce new uses of undef:

• llvm/test/ExecutionEngine/Interpreter/2010-01-15-UndefValue.ll
• llvm/test/ExecutionEngine/Interpreter/test-interp-vec-insertextractvalue.ll
• llvm/test/ExecutionEngine/Interpreter/test-interp-vec-shuffle.ll

Undef is now deprecated and should only be used in the rare cases where no replacement is possible. For example, a load of uninitialized memory yields undef. You should use poison values for placeholders instead.

In tests, avoid using undef and having tests that trigger undefined behavior. If you need an operand with some unimportant value, you can add a new argument to the function and use that instead.

For example, this is considered a bad practice:

define void @fn() {
  ...
  br i1 undef, ...
}

Please use the following instead:

define void @fn(i1 %cond) {
  ...
  br i1 %cond, ...
}

Please refer to the Undefined Behavior Manual for more information.

[asb]

⚠️ undef deprecator found issues in your code. ⚠️

This PR simply moves existing tests, so I think this can reasonably be ignored in the context of this PR (even if in separate work, people might evaluate if undef is desirable or not in these cases).

[preames]

LGTM

[lhames]

LGTM.