[BE] Add regression test for aten shared build (pytorch#96697)

To expose errors similar to pytorch#94401 (comment) in OSS CI

Building `aten_cpu` as a shared library with `-Wl,--no-undefined` simulates behavior of Android NDK toolchain.

Test plan: It should fail, see https://github.com/pytorch/pytorch/actions/runs/4410571970/jobs/7728232916#step:14:1386

Pull Request resolved: pytorch#96697
Approved by: https://github.com/kit1980

.buckconfig.oss

@@ -14,6 +14,7 @@
 
 [cxx]
   cxxflags = -std=c++17
+  ldflags = -Wl,--no-undefined
   should_remap_host_platform = true
   cpp = /usr/bin/clang
   cc = /usr/bin/clang

.github/workflows/_buck-build-test.yml

@@ -73,7 +73,7 @@ jobs:
           timeout_minutes: 10
           max_attempts: 5
           command: |
-            sh scripts/buck_setup.sh
+            bash scripts/buck_setup.sh
 
       - name: Build tools
         run: |
@@ -122,3 +122,7 @@ jobs:
       - name: Build everything
         run: |
           buck build //... --keep-going
+
+      - name: Build aten_cpu@shared
+        run: |
+          buck build :aten_cpu#linux-x86_64,shared