[llvm] [Offload] Add `ol_dimensions_t` (PR #143901)

[Ross Brunton via llvm-commits]

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@@ -148,6 +148,16 @@ def : Struct {
   ];
 }
 
+def : Struct {
+  let name = "ol_dimensions_t";
+  let desc = "A three element vector";
+  let members = [
+    StructMember<"size_t", "x", "X">,
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RossBrunton wrote:

SYCL/UR and OpenCL use u32 for their ranges, while Level Zero seems to use `uint32_t`... I guess it makes sense for Offload to use `uint32_t` as the most widely supported; I'll change it.

https://github.com/llvm/llvm-project/pull/143901