use a more portable no backup argument to patch

Use the --posix argument to prevent patch from making backup files
rather than the --no-backup-if-mismatch argument which is specific to
GNU patch and not supported by various *BSD implementations.

conda_build/source.py

@@ -926,7 +926,7 @@ def try_apply_patch(patch, patch_args, cwd, stdout, stderr):
         temp_name = os.path.join(
             tempfile.gettempdir(), next(tempfile._get_candidate_names())
         )
-        base_patch_args = ["--no-backup-if-mismatch", "--batch"] + patch_args
+        base_patch_args = ["--posix", "--batch"] + patch_args
         try:
             try_patch_args = base_patch_args[:]
             try_patch_args.append("--dry-run")