scripts/checkpatch.pl: Do not allow assert(0)

scripts/checkpatch.pl: Do not allow assert(0)

Since commit 262a69f428 ("osdep.h: Prohibit disabling assert()
in supported builds") we can not build QEMU with NDEBUG (or
G_DISABLE_ASSERT) defined, thus 'assert(0)' always aborts QEMU.

However some static analyzers / compilers doesn't notice NDEBUG
can't be defined and emit warnings if code is used after an
'assert(0)' call.

Apparently such compiler isn't as clever with G_DISABLE_ASSERT,
so we can silent these warnings by using g_assert_not_reached()
which is easier to read anyway.

In order to avoid these annoying warnings, add a checkpatch rule
to prohibit 'assert(0)'. Suggest using g_assert_not_reached()
instead. For example when reverting the previous patch we get:

  ERROR: use g_assert_not_reached() instead of assert(0)
  #21: FILE: target/ppc/dfp_helper.c:124:
  +            assert(0); /* cannot get here */

  ERROR: use g_assert_not_reached() instead of assert(0)
  #30: FILE: target/ppc/dfp_helper.c:141:
  +            assert(0); /* cannot get here */

  total: 2 errors, 0 warnings, 16 lines checked

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230221232520.14480-3-philmd@linaro.org>