LLVM-12 fix for shm_mutex (#65781)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65781
Fixes
```
stderr: In file included from caffe2/caffe2/contrib/shm_mutex/shm_mutex.cc:1:
caffe2/caffe2/contrib/shm_mutex/shm_mutex.h:334:28: error: anonymous non-C-compatible type given name for linkage purposes by alias declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]
using TicketStruct = struct : ShmBaseHeader {
^
TicketStruct
caffe2/caffe2/contrib/shm_mutex/shm_mutex.h:334:31: note: type is not C-compatible due to this base class
using TicketStruct = struct : ShmBaseHeader {
^~~~~~~~~~~~~
caffe2/caffe2/contrib/shm_mutex/shm_mutex.h:334:7: note: type is given name 'TicketStruct' for linkage purposes by this alias declaration
using TicketStruct = struct : ShmBaseHeader {
^
1 error generated.
Cannot execute a rule out of process. On RE worker. Thread: Thread[main,5,main]
Command failed with exit code 1.
```
Test Plan: Sandcastle
Reviewed By: ngimel
Differential Revision: D31248938
fbshipit-source-id: 47342fecc72ada9397a1b7bd6fcabfccf988dd3e
