llvm: disable libomptarget AMDGPU plugin (#42265)

Fixes CI on develop

var/spack/repos/builtin/packages/llvm/package.py

@@ -841,6 +841,12 @@ def cmake_args(self):
 
         cmake_args.append(from_variant("LIBOMPTARGET_ENABLE_DEBUG", "libomptarget_debug"))
 
+        if spec.satisfies("@14:"):
+            # The hsa-rocr-dev package may be pulled in through hwloc, which can lead to cmake
+            # finding libhsa and enabling the AMDGPU plugin. Since we don't support this yet,
+            # disable explicitly. See commit a05a0c3c2f8eefc80d84b7a87a23a4452d4a3087.
+            cmake_args.append(define("LIBOMPTARGET_BUILD_AMDGPU_PLUGIN", False))
+
         if "+lldb" in spec:
             projects.append("lldb")
             cmake_args.extend(