tools/configurator: fix compile error with -O2

In file included from /usr/include/string.h:495,
                 from configuratortest.c:2:
In function ‘strncpy’,
    inlined from ‘main’ at configuratortest.c:6:2:
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: warning: ‘__builtin_strncpy’ specified bound 8 equals destination size [-Wstringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tools/configurator/configurator.c

@@ -411,7 +411,7 @@ static const struct test base_tests[] = {
 	  "int main(int argc, char *argv[]) {\n"
 	  "	(void)argc;\n"
 	  "     char pad[sizeof(int *) * 1];\n"
-	  "	strncpy(pad, argv[0], sizeof(pad));\n"
+	  "	memcpy(pad, argv[0], sizeof(pad));\n"
 	  "	int *x = (int *)pad, *y = (int *)(pad + 1);\n"
 	  "	return *x == *y;\n"
 	  "}\n" },