[BOLT][NFC] Fix data race in ShrinkWrapping stats

Fix data race reported by ThreadSanitizer in clang.test:
```
ThreadSanitizer: data race /data/llvm-project/bolt/lib/Passes/ShrinkWrapping.cpp:1359:28
in llvm::bolt::ShrinkWrapping::moveSaveRestores()
```

The issue is with incrementing global counters from multiple threads.

Reviewed By: yota9

Differential Revision: https://reviews.llvm.org/D120218