Ignore MSVC's pdb file (#47963)
Summary:
These files are generated by MSVC when building with debug symbols `REL_WITH_DEB_INFO=1`:
```
PS C:\Users\Xiang Gao\source\repos\pytorch> git status
On branch master
Your branch is up to date with 'origin/master'.
Untracked files:
(use "git add <file>..." to include in what will be committed)
torch/lib/asmjit.pdb
torch/lib/c10.pdb
torch/lib/c10_cuda.pdb
torch/lib/caffe2_detectron_ops_gpu.pdb
torch/lib/caffe2_module_test_dynamic.pdb
torch/lib/caffe2_observers.pdb
torch/lib/fbgemm.pdb
torch/lib/shm.pdb
torch/lib/torch_cpu.pdb
torch/lib/torch_cuda.pdb
nothing added to commit but untracked files present (use "git add" to track)
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47963
Reviewed By: heitorschueroff
Differential Revision: D25311564
Pulled By: malfet
fbshipit-source-id: 1a7125f3c6ff296b4bb0975ee97b59c23586b1cb
