[llvm] [Offload] Add `MAX_WORK_GROUP_SIZE` device info query (PR #143718)

[Ross Brunton via llvm-commits]

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@@ -264,13 +266,16 @@ Error olGetDeviceInfoImplDetail(ol_device_handle_t Device,
 
     return "";
   };
-  auto GetInfoXyz = [&](std::vector<std::string> Names) {
-    if (!Device->Device)
-      return ol_dimensions_t{0, 0, 0};
+  auto GetInfoXyz = [&](std::vector<std::string> Names) -> Error {
+    if (Device == OffloadContext::get().HostDevice())
+      return ReturnValue(ol_dimensions_t{0u, 0u, 0u});
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RossBrunton wrote:

`ReturnValue` is a helper object with an `operator()` that automatically writes the value to `PropValue` and `PropSizeRet` as appropriate (as well as doing some validation checks).

If this were to return `Expected<ol_dimensions_t>`, then the callers would have to do the Error unwrapping themselves.

@callumfare For the sake of clarity, do you mind if (in a separate patch) I rename this to something like `SetOutput`?

https://github.com/llvm/llvm-project/pull/143718