x86, ptrace: fix build breakage with gcc 4.7

x86, ptrace: fix build breakage with gcc 4.7

Christoph Biedl reported that 2.6.32 does not build with gcc 4.7 on
i386 :

  CC      arch/x86/kernel/ptrace.o
arch/x86/kernel/ptrace.c:1472:17: error: conflicting types for 'syscall_trace_enter'
In file included from /«PKGBUILDDIR»/arch/x86/include/asm/vm86.h:130:0,
                 from /«PKGBUILDDIR»/arch/x86/include/asm/processor.h:10,
                 from /«PKGBUILDDIR»/arch/x86/include/asm/thread_info.h:22,
                 from include/linux/thread_info.h:56,
                 from include/linux/preempt.h:9,
                 from include/linux/spinlock.h:50,
                 from include/linux/seqlock.h:29,
                 from include/linux/time.h:8,
                 from include/linux/timex.h:56,
                 from include/linux/sched.h:56,
                 from arch/x86/kernel/ptrace.c:11:
/«PKGBUILDDIR»/arch/x86/include/asm/ptrace.h:145:13: note: previous declaration of 'syscall_trace_enter' was here
arch/x86/kernel/ptrace.c:1517:17: error: conflicting types for 'syscall_trace_leave'
In file included from /«PKGBUILDDIR»/arch/x86/include/asm/vm86.h:130:0,
                 from /«PKGBUILDDIR»/arch/x86/include/asm/processor.h:10,
                 from /«PKGBUILDDIR»/arch/x86/include/asm/thread_info.h:22,
                 from include/linux/thread_info.h:56,
                 from include/linux/preempt.h:9,
                 from include/linux/spinlock.h:50,
                 from include/linux/seqlock.h:29,
                 from include/linux/time.h:8,
                 from include/linux/timex.h:56,
                 from include/linux/sched.h:56,
                 from arch/x86/kernel/ptrace.c:11:
/«PKGBUILDDIR»/arch/x86/include/asm/ptrace.h:146:13: note: previous declaration of 'syscall_trace_leave' was here
make[4]: *** [arch/x86/kernel/ptrace.o] Error 1
make[3]: *** [arch/x86/kernel] Error 2
make[3]: *** Waiting for unfinished jobs....

He also found that this issue did not appear in more recent kernels since
this asmregparm disappeared in 3.0-rc1 with commit 1b4ac2a935 that was
applied after some UM changes that we don't necessarily want in 2.6.32.

Thus, the cleanest fix for older kernels is to make the declaration in
ptrace.h match the one in ptrace.c by specifying asmregparm on these
functions. They're only called from asm which explains why it used to
work despite the inconsistency in the declaration.

Reported-by: Christoph Biedl <linux-kernel.bfrz@manchmal.in-ulm.de>
Tested-by: Christoph Biedl <linux-kernel.bfrz@manchmal.in-ulm.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>