clang-3.8 fails to compile inline asm having ldarx with 4 args.

Quoting [1]:
'''
Recent versions of the PowerPC architecture added a hint bit to the larx
instructions to differentiate between an atomic operation and a lock
operation:

> 0 Other programs might attempt to modify the word in storage addressed by EA
> even if the subsequent Store Conditional succeeds.
>
> 1 Other programs will not attempt to modify the word in storage addressed by
> EA until the program that has acquired the lock performs a subsequent
> store releasing the lock.
'''

I also found some more info about this in [2].

Anyway, we could either construct some preprocessor logic to omit this
argument for clang, or just drop it. This patch does the latter.

[1] https://patchwork.ozlabs.org/patch/45008/
[2] https://sourceware.org/ml/libc-alpha/2015-03/msg00085.html

travis-ci: success for PPC+clang compile fixes
Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>