Reduce PDB size for storage_grpc feature

We got
```
LINK : fatal error LNK1201: error writing to program database 'C:\b\google\cloud\storage\benchmarks\storage_throughput_vs_cpu_benchmark.pdb'; check for insufficient disk space, invalid path, or insufficient privilege
```
when building `core` feature for `storage_grpc` in `debug` mode.

We cannot use larger runner because the cost is high.

We need to research any way to reduce the PDB size of storage_grpc debug build.