tools/lib/lockdep: Add missing declaration of 'pr_cont()'

Commit:

  681fbec8 ("lockdep: Use consistent printing primitives")

has moved lockdep away from using printk() for printing.

The commit added usage of pr_cont() which wasn't wrapped in the
userspace headers, causing the following warning for the
liblockdep build:

	../../../kernel/locking/lockdep.c:3544:2: warning: implicit declaration of function 'pr_cont' [-Wimplicit-function-declaration]

Adding an empty declaration of 'pr_cont' fixes the problem.

Signed-off-by: Mengting Zhang <zhangmengting@huawei.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: a.p.zijlstra@chello.nl
Link: http://lkml.kernel.org/r/20171212181644.11913-2-alexander.levin@verizon.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>