vsprintf: Use __diag macros to disable '-Wsuggest-attribute=format'

vsprintf: Use __diag macros to disable '-Wsuggest-attribute=format'

The GCC specific warning '-Wsuggest-attribute=format' is disabled around
va_format() using raw #pragma statements, which includes an
'#ifndef __clang__' to avoid a warning about an unknown warning option
from clang (which recognizes '#pragma GCC' for compatibility reasons):

  lib/vsprintf.c:1703:32: error: unknown warning group '-Wsuggest-attribute=format', ignored [-Werror,-Wunknown-warning-option]
   1703 | #pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
        |                                ^

While the current solution works, it is not visually appealing. The
kernel already has some infrastructure that wraps these #pragma
statements to give more specific control over diagnostics without
needing #ifdef blocks for different compilers. Convert the existing
statements over to the __diag macros.

Closes: https://lore.kernel.org/r/CAHk-=wgfX9nBGE0Ap9GjhOy7Mn=RSy=rx0MvqfYFFDx31KJXqQ@mail.gmail.com
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20250404-vsprintf-convert-pragmas-to-__diag-v1-2-5d6c5c55b2bd@kernel.org
Signed-off-by: Petr Mladek <pmladek@suse.com>