clang: arch/x86/boot/printf.c:257:3: error: unannotated fall-through between switch labels [-Werror,-Wimplicit-fallthrough]

[Naresh Kamboju]

The following x86 build failed on Linux next-20240517 tag due to following
warnings / errors only seen with clang builds.

Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>

Build errors:
----
arch/x86/boot/printf.c:257:3: error: unannotated fall-through between
switch labels [-Werror,-Wimplicit-fallthrough]
  257 |                 case 'u':
      |                 ^
arch/x86/boot/printf.c:257:3: note: insert 'break;' to avoid fall-through
  257 |                 case 'u':
      |                 ^
      |                 break;
1 error generated.

The suspected patch,
x86/boot: Add a fallthrough annotation

metadata:
---
  git_describe: next-20240517
  git_repo: https://gitlab.com/Linaro/lkft/mirrors/next/linux-next
  git_sha: c75962170e49f24399141276ae119e6a879f36dc
  git_short_log: c75962170e49 ("Add linux-next specific files for 20240517")
  build_name: clang-18-lkftconfig


Links:
 - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20240517/testrun/23951572/suite/build/test/clang-18-lkftconfig/log
 - https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20240517/testrun/23951572/suite/build/test/clang-18-lkftconfig/details/
 - https://storage.tuxsuite.com/public/linaro/lkft/builds/2gZwb1q4GHgVCuOfQIMCJ6tqMFn/


--
Linaro LKFT
https://lkft.linaro.org