Tell Bazel the specific target version of macOS too. Sigh.

Change-Id: I4f50d5299a0462d279042a2175995fff00ff97e4
Reviewed-on: https://code-review.googlesource.com/c/re2/+/62912
Reviewed-by: Paul Wankadia <junyer@google.com>
Reviewed-by: Jeff Bailey <jeffbailey@google.com>

python/setup.py

@@ -61,6 +61,11 @@ class BuildExt(setuptools.command.build_ext.build_ext):
         cmd.append(f'--extra_toolchains=@local_config_cc//:cc-toolchain-{cpu}')
     except KeyError:
       pass
+    try:
+      ver = os.environ['MACOSX_DEPLOYMENT_TARGET']
+      cmd.append(f'--macos_minimum_os={ver}')
+    except KeyError:
+      pass
     # Register the local Python toolchains with highest priority.
     self.generate_python_toolchains()
     cmd.append('--extra_toolchains=//python/toolchains:all')