A few panic() related functions have a global definition but not
declaration, which causes a warning with W=1:

kernel/panic.c:710:6: error: no previous prototype for '__warn_printk' [-Werror=missing-prototypes]
kernel/panic.c:756:24: error: no previous prototype for '__stack_chk_fail' [-Werror=missing-prototypes]
kernel/exit.c:1917:32: error: no previous prototype for 'abort' [-Werror=missing-prototypes]

__warn_printk() is called both as a global function when CONFIG_BUG
is enabled, and as a local function in other configs. The other
two here are called indirectly from generated or assembler code.

Add prototypes for all of these.

Link: https://lkml.kernel.org/r/20230517131102.934196-9-arnd@kernel.orgSigned-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Eric Paris <eparis@redhat.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>