ensure the avr example keeps compiling (#17663)

* ensure the avr example keeps compiling

* Update tests/avr/thello.nim

* now compiles properly

tests/avr/panicoverride.nim

@@ -0,0 +1,13 @@
+proc printf(frmt: cstring) {.varargs, importc, header: "<stdio.h>", cdecl.}
+proc exit(code: int) {.importc, header: "<stdlib.h>", cdecl.}
+
+{.push stack_trace: off, profiler:off.}
+
+proc rawoutput(s: string) =
+  printf("%s\n", s)
+
+proc panic(s: string) =
+  rawoutput(s)
+  exit(1)
+
+{.pop.}