Skip io_uring feature test when building with fbcode (#12525)

Skip io_uring feature test when building with fbcode (#12525)

Summary:
Previously when building with fbcode and having a system install of liburing, it would link liburing from fbcode statically as well as the system library dynamically. That led to the following error:

```
./db_stress: error while loading shared libraries: liburing.so.1: cannot open shared object file: No such file or directory
```

The fix is to skip the feature test for system liburing when `FBCODE_BUILD=true`.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/12525

Test Plan:
- `make clean && make ROCKSDB_NO_FBCODE=1 V=1 -j56 db_stress && ./db_stress`
- `make clean && make V=1 -j56 db_stress && ./db_stress`

Reviewed By: anand1976

Differential Revision: D55997335

Pulled By: ajkr

fbshipit-source-id: 17d8561100f41c6c9ae382a80c6cddc14f050bdc