x86: headers cleanup - prctl.h

Impact: cleanup (internal kernel function exported)

'make headers_check' warn us about leaking of kernel private
(mostly compile time vars) data to userspace in headers. Fix it.

sys_arch_prctl is completely removed from
header since frankly I don't even understand why we
describe it here. It is described like
__SYSCALL(__NR_arch_prctl, sys_arch_prctl) in unistd_64.h
and implemented in process_64.c. User-mode linux involved?
So this one in fact is suspicious.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/prctl.h

@@ -6,8 +6,4 @@
 #define ARCH_GET_FS 0x1003
 #define ARCH_GET_GS 0x1004
 
-#ifdef CONFIG_X86_64
-extern long sys_arch_prctl(int, unsigned long);
-#endif /* CONFIG_X86_64 */
-
 #endif /* _ASM_X86_PRCTL_H */