Link in XLA for open source OSX builds by default

PiperOrigin-RevId: 254235029
diff --git a/configure.py b/configure.py
index a475c02..55d7897 100644
--- a/configure.py
+++ b/configure.py
@@ -1426,7 +1426,7 @@
   if is_ppc64le():
     write_action_env_to_bazelrc('OMP_NUM_THREADS', 1)
 
-  xla_enabled_by_default = is_linux()
+  xla_enabled_by_default = is_linux() or is_macos()
   set_build_var(environ_cp, 'TF_ENABLE_XLA', 'XLA JIT', 'with_xla_support',
                 xla_enabled_by_default, 'xla')