fixed after suggestion from Kuba

Author: Carl Peto

utils/build_swift/build_swift/driver_arguments.py

@@ -1355,7 +1355,7 @@ def create_argument_parser():
            help='enable building llvm using modules')
 
     option('--llvm-targets-to-build', store,
-           default='X86;ARM;AArch64;PowerPC;SystemZ;Mips;RISCV;WebAssembly',
+           default='X86;ARM;AArch64;PowerPC;SystemZ;Mips;RISCV;WebAssembly;AVR',
            help='LLVM target generators to build')
 
     option('--llvm-ninja-targets', append,