gcc 10.x compile warning/error for array subscript 0 is outside the bounds in tests/bluetooth/tester/src/gap.c

[galak]

When building tests/bluetooth/tester on qemu_x86 with gcc 10.2 we get:

/home/galak/git/zephyr/tests/bluetooth/tester/src/gap.c: In function 'tester_handle_gap':
/home/galak/git/zephyr/tests/bluetooth/tester/src/gap.c:278:35: error: array subscript 254 is outside the bounds of an interior zero-length array 'const uint8_t[0]' {aka 'const unsigned char[]'} [-Werror=zero-length-bounds]
  278 |   ad[adv_len].type = cmd->adv_data[i++];
      |                      ~~~~~~~~~~~~~^~~~~
In file included from /home/galak/git/zephyr/tests/bluetooth/tester/src/gap.c:25:
/home/galak/git/zephyr/tests/bluetooth/tester/src/bttester.h:157:10: note: while referencing 'adv_data'
  157 |  uint8_t adv_data[0];
      |          ^~~~~~~~
/home/galak/git/zephyr/tests/bluetooth/tester/src/gap.c:279:39: error: array subscript 255 is outside the bounds of an interior zero-length array 'const uint8_t[0]' {aka 'const unsigned char[]'} [-Werror=zero-length-bounds]
  279 |   ad[adv_len].data_len = cmd->adv_data[i++];
      |                          ~~~~~~~~~~~~~^~~~~
In file included from /home/galak/git/zephyr/tests/bluetooth/tester/src/gap.c:25:
/home/galak/git/zephyr/tests/bluetooth/tester/src/bttester.h:157:10: note: while referencing 'adv_data'
  157 |  uint8_t adv_data[0];
      |          ^~~~~~~~
/home/galak/git/zephyr/tests/bluetooth/tester/src/gap.c:280:22: error: array subscript 256 is outside the bounds of an interior zero-length array 'const uint8_t[0]' {aka 'const unsigned char[]'} [-Werror=zero-length-bounds]
  280 |   ad[adv_len].data = &cmd->adv_data[i];
      |                      ^~~~~~~~~~~~~~~~~
In file included from /home/galak/git/zephyr/tests/bluetooth/tester/src/gap.c:25:
/home/galak/git/zephyr/tests/bluetooth/tester/src/bttester.h:157:10: note: while referencing 'adv_data'
  157 |  uint8_t adv_data[0];
      |          ^~~~~~~~
cc1: all warnings being treated as errors