This warning option still produces output on gcc but is now clean when
building with clang, so enable it conditionally on the compiler for now.

As far as I can tell, the remaining warnings with gcc are the result of
analysing the code more deeply across inlining, while clang only does this
within a function.

Link: https://lore.kernel.org/lkml/20240326230511.GA2796782@dev-arch.thelio-3990X/
Link: https://lore.kernel.org/linux-patches/20231002-disable-wformat-truncation-overflow-non-kprintf-v1-1-35179205c8d9@kernel.org/
Link: https://lkml.kernel.org/r/20240415122037.1983124-5-arnd@kernel.orgSigned-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>