tools: Disable __packed attribute compiler warning due to -Werror=attributes

Noticed on several perf tools cross build test containers:

  [perfbuilder@five ~]$ grep FAIL ~/dm.log/summary
    19    10.18 debian:experimental-x-mips    : FAIL gcc version 12.3.0 (Debian 12.3.0-6)
    20    11.21 debian:experimental-x-mips64  : FAIL gcc version 12.3.0 (Debian 12.3.0-6)
    21    11.30 debian:experimental-x-mipsel  : FAIL gcc version 12.3.0 (Debian 12.3.0-6)
    37    12.07 ubuntu:18.04-x-arm            : FAIL gcc version 7.5.0 (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04)
    42    11.91 ubuntu:18.04-x-riscv64        : FAIL gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)
    44    13.17 ubuntu:18.04-x-sh4            : FAIL gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)
    45    12.09 ubuntu:18.04-x-sparc64        : FAIL gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)
  [perfbuilder@five ~]$

  In file included from util/intel-pt-decoder/intel-pt-pkt-decoder.c:10:
  /tmp/perf-6.6.0-rc1/tools/include/asm-generic/unali...