Set MACOSX_DEPLOYMENT_TARGET=10.9 in binary build jobs (#2546)

Summary:
Recent CircleCI migration https://github.com/pytorch/audio/pull/2529
silently bumped the minimum supported macOS version to 11.

PyTorch still supports 10.9 and the ecosystem still uses 10.9.
Issue: https://github.com/pytorch/audio/issues/2536

This commit sets MACOSX_DEPLOYMENT_TARGET=10.9, so that binary
distribution are compatible on macOS=10.9.

Pull Request resolved: https://github.com/pytorch/audio/pull/2546

Reviewed By: atalman

Differential Revision: D37854586

Pulled By: mthrok

fbshipit-source-id: a43986ae4de9ef51a4261e0f9fe58e88b4b72148

.circleci/config.yml

@@ -86,6 +86,7 @@ binary_common: &binary_common
     BUILD_VERSION: << parameters.build_version >>
     PYTORCH_VERSION: << parameters.pytorch_version >>
     CU_VERSION: << parameters.cuda_version >>
+    MACOSX_DEPLOYMENT_TARGET: 10.9
 
 smoke_test_common: &smoke_test_common
   <<: *binary_common

.circleci/config.yml.in

@@ -86,6 +86,7 @@ binary_common: &binary_common
     BUILD_VERSION: << parameters.build_version >>
     PYTORCH_VERSION: << parameters.pytorch_version >>
     CU_VERSION: << parameters.cuda_version >>
+    MACOSX_DEPLOYMENT_TARGET: 10.9
 
 smoke_test_common: &smoke_test_common
   <<: *binary_common

packaging/torchaudio/meta.yaml

@@ -49,6 +49,7 @@ build:
     - USE_FFMPEG
     - USE_OPENMP
     - FFMPEG_ROOT
+    - MACOSX_DEPLOYMENT_TARGET
 
 test:
   imports: