[AARCH64][CD][CUDA13][Triton][PTXAS] Turn on BUILD_BUNDLE_PTXAS=1 (#163988)

See also #163972, which was intended to be this PR.

Triton (release/3.5.x) by default ships CUDA12.8 ptxas.
This PR tries to bundle a ptxas version for cuda13, so that it can help https://github.com/pytorch/pytorch/issues/163801 when users run on new devices like THOR and Spark.

Fixes https://github.com/pytorch/pytorch/issues/163801

Test Plan:

Check binary size increase against nightly or v2.9RC
Install the binary from into a working THOR and GB200/GH100 machine (reproduce the original issue first on THOR), then install the binary built from this PR and we expect the issue to be gone without any additional user setting. Testing on GB200 is to ensure no regression.
Reference: https://github.com/pytorch/pytorch/pull/119750 and 5c814e2527

Note: with this PR, the pytorch world's torch.compile is supposed to find ptxas via "torch/_inductor/runtime/compile_tasks.py" and "_set_triton_ptxas_path". Use cases that do not go through "_set_triton_ptxas_path" may not be able to use the cuda13 ptxas binary.
However, as is, the triton world does not know the existence of this new cuda13 ptxas. So IF a users thinks there is already pytorch/bin/ptxas and delete the ptxas from triton, then  c6ad34f7eb/python/triton/knobs.py (L216) would still complain ptxas not found (if removed - it won't know this new one available)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/163988
Approved by: https://github.com/atalman

.ci/aarch64_linux/aarch64_ci_build.sh

@@ -15,6 +15,8 @@ fi
 # Compress the fatbin with -compress-mode=size for CUDA 13
 if [[ "$DESIRED_CUDA" == *"13"* ]]; then
     export TORCH_NVCC_FLAGS="-compress-mode=size"
+    # Bundle ptxas into the cu13 wheel, see https://github.com/pytorch/pytorch/issues/163801
+    export BUILD_BUNDLE_PTXAS=1
 fi
 
 SCRIPTPATH="$( cd -- "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"

torch/_inductor/runtime/compile_tasks.py

@@ -40,7 +40,7 @@ def _reload_python_module(
 def _set_triton_ptxas_path() -> None:
     if os.environ.get("TRITON_PTXAS_PATH") is not None:
         return
-    ptxas = Path(__file__).absolute().parents[1] / "bin" / "ptxas"
+    ptxas = Path(__file__).absolute().parents[2] / "bin" / "ptxas"
     if not ptxas.exists():
         return
     if ptxas.is_file() and os.access(ptxas, os.X_OK):