`torchao:` quantization schemes can't find ao lib

🐛 Describe the bug

Anytime _load_torchao_aten_lib is called (namely for -qmode 8da[]w), the following error pops up:

Traceback (most recent call last):
File "/home/jackzhxng/.conda/envs/oss2/lib/python3.10/runpy.py", line 196, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/home/jackzhxng/.conda/envs/oss2/lib/python3.10/runpy.py", line 86, in _run_code
exec(code, run_globals)
File "/home/jackzhxng/torchrepos2/executorch/examples/models/llama/runner/eager.py", line 116, in
main() # pragma: no cover
File "/home/jackzhxng/torchrepos2/executorch/examples/models/llama/runner/eager.py", line 112, in main
execute_runner(EagerLlamaRunner)
File "/home/jackzhxng/torchrepos2/executorch/examples/models/llama/runner/eager.py", line 93, in execute_runner
runner = runner_class(args) # pyre-ignore: Missing argument [20]
File "/home/jackzhxng/torchrepos2/executorch/examples/models/llama/runner/eager.py", line 38, in init
manager: LLMEdgeManager = _prepare_for_llama_export(args)
File "/home/jackzhxng/.conda/envs/oss2/lib/python3.10/site-packages/executorch/examples/models/llama/export_llama_lib.py", line 601, in _prepare_for_llama_export
.source_transform(_get_source_transforms(args.model, dtype_override, args))
File "/home/jackzhxng/.conda/envs/oss2/lib/python3.10/site-packages/executorch/extension/llm/export/builder.py", line 154, in source_transform
self.model = transform(self.model)
File "/home/jackzhxng/.conda/envs/oss2/lib/python3.10/site-packages/executorch/examples/models/llama/source_transformation/quantize.py", line 101, in quantize
_load_torchao_aten_lib(libname="libtorchao_ops_aten")
File "/home/jackzhxng/.conda/envs/oss2/lib/python3.10/site-packages/executorch/examples/models/llama/source_transformation/quantize.py", line 823, in _load_torchao_aten_lib
assert (
AssertionError: Expected 1 library but got 0. If you installed the torchao ops in a non-standard location, please set CMAKE_INSTALL_PREFIX correctly.

Versions

PyTorch version: 2.7.0.dev20250131+cpu
Is debug build: False
CUDA used to build PyTorch: None
ROCM used to build PyTorch: N/A

OS: CentOS Stream 9 (x86_64)
GCC version: (GCC) 11.5.0 20240719 (Red Hat 11.5.0-2)
Clang version: Could not collect
CMake version: version 3.30.5
Libc version: glibc-2.34

Python version: 3.10.0 (default, Mar 3 2022, 09:58:08) [GCC 7.5.0] (64-bit runtime)
Python platform: Linux-6.4.3-0_fbk12_hardened_2624_g7d95a0297d81-x86_64-with-glibc2.34
Is CUDA available: False
CUDA runtime version: No CUDA
CUDA_MODULE_LOADING set to: N/A
GPU models and configuration: No CUDA
Nvidia driver version: No CUDA
cuDNN version: No CUDA
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: True

CPU:
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Address sizes: 40 bits physical, 57 bits virtual
Byte Order: Little Endian
CPU(s): 166
On-line CPU(s) list: 0-165
Vendor ID: AuthenticAMD
Model name: AMD EPYC-Milan Processor
CPU family: 25
Model: 1
Thread(s) per core: 2
Core(s) per socket: 83
Socket(s): 1
Stepping: 1
BogoMIPS: 2399.99
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm rep_good nopl cpuid extd_apicid tsc_known_freq pni pclmulqdq ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm cmp_legacy svm cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw topoext perfctr_core invpcid_single ssbd ibrs ibpb stibp vmmcall fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves avx512_bf16 clzero xsaveerptr wbnoinvd arat npt lbrv nrip_save tsc_scale vmcb_clean pausefilter pfthreshold avx512vbmi umip pku ospke avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg avx512_vpopcntdq rdpid fsrm arch_capabilities
Virtualization: AMD-V
Hypervisor vendor: KVM
Virtualization type: full
L1d cache: 2.6 MiB (83 instances)
L1i cache: 2.6 MiB (83 instances)
L2 cache: 41.5 MiB (83 instances)
L3 cache: 32 MiB (1 instance)
NUMA node(s): 1
NUMA node0 CPU(s): 0-165
Vulnerability Gather data sampling: Not affected
Vulnerability Itlb multihit: Not affected
Vulnerability L1tf: Not affected
Vulnerability Mds: Not affected
Vulnerability Meltdown: Not affected
Vulnerability Mmio stale data: Not affected
Vulnerability Retbleed: Not affected
Vulnerability Spec store bypass: Vulnerable
Vulnerability Spectre v1: Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers
Vulnerability Spectre v2: Vulnerable, IBPB: disabled, STIBP: disabled, PBRSB-eIBRS: Not affected
Vulnerability Srbds: Not affected
Vulnerability Tsx async abort: Not affected

Versions of relevant libraries:
[pip3] executorch==0.6.0a0+bb60a20
[pip3] flake8==6.1.0
[pip3] flake8-breakpoint==1.1.0
[pip3] flake8-bugbear==24.4.26
[pip3] flake8-comprehensions==3.14.0
[pip3] flake8-plugin-utils==1.3.3
[pip3] flake8-pyi==23.5.0
[pip3] mypy==1.14.1
[pip3] mypy-extensions==1.0.0
[pip3] numpy==2.2.2
[pip3] torch==2.7.0.dev20250131+cpu
[pip3] torchao==0.10.0+git7d879462
[pip3] torchaudio==2.6.0.dev20250131+cpu
[pip3] torchsr==1.0.4
[pip3] torchtune==0.0.0
[pip3] torchvision==0.22.0.dev20250131+cpu
[conda] executorch 0.6.0a0+bb60a20 pypi_0 pypi
[conda] numpy 2.2.2 pypi_0 pypi
[conda] torch 2.7.0.dev20250131+cpu pypi_0 pypi
[conda] torchao 0.10.0+git7d879462 pypi_0 pypi
[conda] torchaudio 2.6.0.dev20250131+cpu pypi_0 pypi
[conda] torchfix 0.6.0 pypi_0 pypi
[conda] torchsr 1.0.4 pypi_0 pypi
[conda] torchtune 0.0.0 pypi_0 pypi
[conda] torchvision 0.22.0.dev20250131+cpu pypi_0 pypi

cc @kimishpatel @jerryzh168

Start in examples/models/llama/source_transformation/quantize.py at _load_torchao_aten_lib, especially the call around line 811 and the assertion around line 823. Reproduce the -qmode 8da[]w path and inspect how the torchao library location and CMAKE_INSTALL_PREFIX are discovered. Done means the quantization scheme finds the expected library instead of reporting zero libraries.