[llvm] [Offload] Skip most liboffload tests if no devices (PR #157417)

[Ross Brunton via llvm-commits]

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@@ -129,6 +129,9 @@ const std::vector<TestEnvironment::Device> &TestEnvironment::getDevices() {
     }
   }
 
+  if (Devices.size() <= 1)
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RossBrunton wrote:

Ah, thanks. I completely missed that the host device was being excluded. It's now `== 0`, which seems to work.

https://github.com/llvm/llvm-project/pull/157417