compat: fixes to allow working with tile arch

The existing <asm-generic/unistd.h> mechanism doesn't really provide
enough to create the 64-bit "compat" ABI properly in a generic way,
since the compat ABI is a mix of things were you can re-use the 64-bit
versions of syscalls and things where you need a compat wrapper.

To provide this in the most direct way possible, I added two new macros
to go along with the existing __SYSCALL and __SC_3264 macros: __SC_COMP
and SC_COMP_3264.  These macros take an additional argument, typically a
"compat_sys_xxx" function, which is passed to __SYSCALL if you define
__SYSCALL_COMPAT when including the header, resulting in a pointer to
the compat function being placed in the generated syscall table.

The change also adds some missing definitions to <linux/compat.h> so that
it actually has declarations for all the compat syscalls, since the
"[nr] = ##call" approach requires proper C declarations for all the
functions included in the syscall table.

Finally, compat.c defines compat_sys_sigpending() and
compat_sys_sigprocmask() even if the underlying architecture doesn't
request it, which tries to pull in undefined compat_old_sigset_t defines.
We need to guard those compat syscall definitions with appropriate
__ARCH_WANT_SYS_xxx ifdefs.
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/kernel/compat.c

@@ -135,7 +135,7 @@ long tile_compat_sys_msgrcv(int msqid,
 
 /* Provide the compat syscall number to call mapping. */
 #undef __SYSCALL
-#define __SYSCALL(nr, call) [nr] = (compat_##call),
+#define __SYSCALL(nr, call) [nr] = (call),
 
 /* The generic versions of these don't work for Tile. */
 #define compat_sys_msgrcv tile_compat_sys_msgrcv

kernel/compat.c

@@ -293,6 +293,8 @@ asmlinkage long compat_sys_times(struct compat_tms __user *tbuf)
 	return compat_jiffies_to_clock_t(jiffies);
 }
 
+#ifdef __ARCH_WANT_SYS_SIGPENDING
+
 /*
  * Assumption: old_sigset_t and compat_old_sigset_t are both
  * types that can be passed to put_user()/get_user().
@@ -312,6 +314,10 @@ asmlinkage long compat_sys_sigpending(compat_old_sigset_t __user *set)
 	return ret;
 }
 
+#endif
+
+#ifdef __ARCH_WANT_SYS_SIGPROCMASK
+
 asmlinkage long compat_sys_sigprocmask(int how, compat_old_sigset_t __user *set,
 		compat_old_sigset_t __user *oset)
 {
@@ -333,6 +339,8 @@ asmlinkage long compat_sys_sigprocmask(int how, compat_old_sigset_t __user *set,
 	return ret;
 }
 
+#endif
+
 asmlinkage long compat_sys_setrlimit(unsigned int resource,
 		struct compat_rlimit __user *rlim)
 {