avr: fix default handler in interrupt vector

Apparently the target of a weak symbol must be defined in the same file
as where it is used as a weak symbol.

https://www.avrfreaks.net/forum/using-weak-custom-vector-table#comment-745922

targets/avr.S

@@ -38,16 +38,6 @@ init_data_end:
     ; need to jump.
 
 
-; This is the default handler for interrupts, if triggered but not defined.
-; Sleep inside so that an accidentally triggered interrupt won't drain the
-; battery of a battery-powered device.
-.section .text.__vector_default
-.global  __vector_default
-__vector_default:
-    sleep
-    rjmp __vector_default
-
-
 ; The only thing this WDT handler really does is disable itself, to get out of
 ; sleep mode.
 .section .text.__vector_WDT

tools/gen-device-avr.py

@@ -208,6 +208,15 @@ def writeAsm(outdir, device):
 ; Automatically generated file. DO NOT EDIT.
 ; Generated by gen-device-avr.py from {file}, see {descriptorSource}
 
+; This is the default handler for interrupts, if triggered but not defined.
+; Sleep inside so that an accidentally triggered interrupt won't drain the
+; battery of a battery-powered device.
+.section .text.__vector_default
+.global  __vector_default
+__vector_default:
+    sleep
+    rjmp __vector_default
+
 ; Avoid the need for repeated .weak and .set instructions.
 .macro IRQ handler
     .weak  \\handler