[ORC] Improve JITLinkReentryTrampolines "arch not supported" error message.

"Architecture not supported" becomes
"JITLinkReentryTrampolines: architecture <arch> not supported".

Author: lhames

llvm/lib/ExecutionEngine/Orc/JITLinkReentryTrampolines.cpp

@@ -86,12 +86,14 @@ JITLinkReentryTrampolines::Create(ObjectLinkingLayer &ObjLinkingLayer) {
 
   EmitTrampolineFn EmitTrampoline;
 
-  switch (ObjLinkingLayer.getExecutionSession().getTargetTriple().getArch()) {
+  const auto &TT = ObjLinkingLayer.getExecutionSession().getTargetTriple();
+  switch (TT.getArch()) {
   case Triple::aarch64:
     EmitTrampoline = aarch64::createAnonymousReentryTrampoline;
     break;
   default:
-    return make_error<StringError>("Architecture not supported",
+    return make_error<StringError>("JITLinkReentryTrampolines: architecture " +
+				   TT.getArchName() + " not supported",
                                    inconvertibleErrorCode());
   }