Give devices without PCI topology a stable cache identity

[galekseev]

Summary

The compiled-kernel cache never hit on an Apple GPU. getUniqueDeviceIdentifier asks for CL_DEVICE_PCI_BUS_ID_NV and CL_DEVICE_PCI_SLOT_ID_NV, which Apple's runtime does not implement, and clGetWrapper returned the value it declared without initializing it and without looking at the error code:

template <typename T, typename U, typename V, typename W>
T clGetWrapper(U function, V param, W param2) {
	T t;
	function(param, param2, sizeof(t), &t, NULL);
	return t;
}

So the identifier was whatever was on the stack. Three consecutive runs on an M4 Max wrote three different cache files and every one reported precompiled = no, meaning the kernel was recompiled on every start.

Queries now go through clGetWrapperChecked, which zeroes the value and reports whether the runtime answered. Where neither vendor extension is available, the identifier is an FNV-1a hash of the device name, vendor and driver version. Two identical GPUs hash to one entry, which is correct: the binary they need is the same. Devices that do report PCI topology keep the identifier they had, so caches already on disk stay valid and NVIDIA and AMD see no change.

The same missing check made clGetWrapperString size its buffer from an uninitialized length whenever a query failed.

Two smaller things ride along. The container smoke test had a blind spot: without a GPU the program exits before loading a kernel, so nothing verified the kernels were in the image at all - it now checks they sit next to the binary. And the two bench examples pointed at pr57-head, a branch that only ever existed on one laptop, rather than the portable pr/57.

Test plan

• on an M4 Max, three runs now produce one cache file, with runs 2 and 3 reporting precompiled = yes; before the change it was three files and precompiled = no every time
• make and make -C tests build without warnings, test_correctness_pr49.x64 passes
• the PCI path is untouched, so cache filenames on NVIDIA and AMD are unchanged
• CI builds the image and confirms the kernels are next to the binary in it

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