[compiler-rt] [hwasan] Don't check code model if there are no real globals (PR #131152)

[Thurston Dang via llvm-commits]

thurstond wrote:

> What makes a global real vs unreal?

```
  // Create a zero-length global in hwasan_globals so that the linker will
  // always create start and stop symbols.
```

Zero-length globals aren't real, they can't hurt you

except they can hurt because the runtime will still perform the code model check.

https://github.com/llvm/llvm-project/pull/131152