gcc may throw the following compilation error if UNREACHABLE
is used within a constexpr function:
```
error: call to non-'constexpr' function
                  'void V8_Fatal(const char*, ...)'
```

Bug: v8:11420
Change-Id: I7f8237d00ba1a5d9bd778d45eb833b89cbe8eb24
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2906032
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74688}