llvm-exegesis: Error on MCSubtargetInfo construction failure (#159223)

Author: arsenm

llvm/tools/llvm-exegesis/lib/LlvmState.cpp

@@ -56,6 +56,11 @@ Expected<LLVMState> LLVMState::Create(std::string TripleName,
 
   std::unique_ptr<MCSubtargetInfo> STI(
       TheTarget->createMCSubtargetInfo(TheTriple, CpuName, ""));
+  if (!STI) {
+    return make_error<StringError>("unable to create subtarget info",
+                                   inconvertibleErrorCode());
+  }
+
   assert(STI && "Unable to create subtarget info!");
   if (!STI->isCPUStringValid(CpuName)) {
     return make_error<StringError>(Twine("invalid CPU name (")