S390X: fix detection of magic number placeholder in inductor (pytorch#157784)

This change fixes multiple tests in
test/inductor/test_aot_inductor_arrayref.py
such as
test_cond_with_parameters_cpu_with_stack_allocation,
test_issue_140766_cpu_with_stack_allocation,
test_model_modified_weights_cpu_with_stack_allocation,
test_nested_tensor_from_jagged_cpu_with_stack_allocation.

Enable tests in test/inductor/test_aot_inductor_arrayref.py

This change is split off from pytorch#150116

Pull Request resolved: pytorch#157784
Approved by: https://github.com/huydhn

Author: AlekseiNikiforovIBM

test/run_test.py

@@ -182,7 +182,6 @@ def __contains__(self, item):
     "dynamo/test_misc",
     "inductor/test_cpu_repro",
     "inductor/test_cpu_select_algorithm",
-    "inductor/test_aot_inductor_arrayref",
     "inductor/test_torchinductor_codegen_dynamic_shapes",
     "lazy/test_meta_kernel",
     "onnx/test_utility_funs",

torch/_inductor/codecache.py

@@ -2003,7 +2003,11 @@ def get_zero_consts_asm_code(
                     f.seek(0)
                     hdr = f.read(1024)
                     # Search for magic number and write the actual data over it
-                    start_idx = hdr.find(b"\xef\xcd\xab\x99\x78\x56\x34\x12")
+                    start_idx = (
+                        hdr.find(b"\xef\xcd\xab\x99\x78\x56\x34\x12")
+                        if sys.byteorder == "little"
+                        else hdr.find(b"\x12\x34\x56\x78\x99\xab\xcd\xef")
+                    )
                     assert start_idx != -1
                     f.seek(start_idx)
                     pos = 0