no need for this, AVR supports an implementation of atomic llvm ops

Author: Carl Peto

lib/Basic/LangOptions.cpp

@@ -392,10 +392,6 @@ void LangOptions::setHasAtomicBitWidth(llvm::Triple triple) {
     setMaxAtomicBitWidth(128);
     break;
 
-  case llvm::Triple::ArchType::avr:
-    setMaxAtomicBitWidth(0);
-    break;
-
   default:
     // Some exotic architectures may not support atomics at all. If that's the
     // case please update the switch with your flavor of arch. Otherwise assume