[OpenMP][Fix] Check Expected<T> and assert if fail

This checks the Expected for value. This should probably not fail, and
if it does, I think we can safely abort with a failing assert.

Change-Id: Ia017e1b8e321d8d5f8363d5d76642544f8730405

Author: jplehr

openmp/libomptarget/plugins-nextgen/amdgpu/utils/UtilitiesRTL.h

@@ -140,6 +140,10 @@ extractXnackModeFromBinary(const __tgt_device_image *TgtImage) {
   Expected<ELF64LEObjectFile> ElfOrErr =
       ELF64LEObjectFile::create(MemoryBufferRef(Buffer, /*Identifier=*/""),
                                 /*InitContent=*/false);
+  if (!ElfOrErr) {
+    consumeError(ElfOrErr.takeError());
+    return XNACK_UNSUPPORTED;
+  }
 
   u_int16_t EFlags = ElfOrErr->getELFFile().getHeader().e_flags;
   unsigned XnackFlags = EFlags & ELF::EF_AMDGPU_FEATURE_XNACK_V4;