alpha: take a bunch of syscalls into osf_sys.c

New helper: current_thread_info().  Allows to do a bunch of odd syscalls
in C. While we are at it, there had never been a reason to do
osf_getpriority() in assembler.  We also get "namespace"-aware (read:
consistent with getuid(2), etc.) behaviour from getx?id() syscalls now.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Acked-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/include/asm/ptrace.h

@@ -76,7 +76,10 @@ struct switch_stack {
 #define task_pt_regs(task) \
   ((struct pt_regs *) (task_stack_page(task) + 2*PAGE_SIZE) - 1)
 
-#define force_successful_syscall_return() (task_pt_regs(current)->r0 = 0)
+#define current_pt_regs() \
+  ((struct pt_regs *) ((char *)current_thread_info() + 2*PAGE_SIZE) - 1)
+
+#define force_successful_syscall_return() (current_pt_regs()->r0 = 0)
 
 #endif