[BOLT] Guard llvm-bolt-wrapper logic of NFC-Mode behind a flag (#146209)

Buildbot (`BOLTBuilder`) no longer relies on a wrapper script to run
tests. This
patch guards the wrapper logic under a flag that is disabled by default.
This
it allows to:
- Eliminate the need for special handling in some tests.
- Fix the issue of a wrapper loop (described below)
- Simplify the NFC-Mode setup.

**Background:**
Previously, tests ran unconditionally, which also compiled any missing
utilities
and the unit tests.

The `nfc-check-setup.py` created:
- `llvm-bolt.new`, renamed from the current compilation
- `llvm-bolt.old`, built from the previous SHA
- `llvm-bolt`: a python wrapper pointing to `llvm-bolt.new`

Current behaviour and wrapper issue:
As before, the old/new binaries identify whether a patch affects BOLT.
If so,
`ninja check-bolt` builds missing dependencies and run tests,
overwriting the
`llvm-bolt` wrapper with a binary.

However, if Ninja reports:
```
ninja: no work to do.
```

the wrapper remains in place. If the next commit also does no work,
`nfc-check-setup.py` renames the existing wrapper to `llvm-bolt.new`,
causing an
infinite loop.

Allowing to disable the wrapper logic prevents this scenario and
simplifies the flow.


**Test plan:**

Creates llvm-bolt.new and llvm-bolt.old and stays on previous revision:
```
./nfc-check-setup.py build
```

Creates llvm-bolt.new and llvm-bolt.old and returns on current revision:
```
./nfc-check-setup.py build --switch-back
```

Creates llvm-bolt.new and llvm-bolt.old, returns on current revision,
and
creates a wrapper:
```
./nfc-check-setup.py build --switch-back --create-wrapper
```

Creates llvm-bolt.new and llvm-bolt.old, and passes an invalid argument
to the
wrapper:
```
./nfc-check-setup.py build --switch-back --create-wrapper --random-arg
```

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