seccomp: allow COMPAT sigreturn overrides

Most architectures don't need to do much special for the strict-mode
seccomp syscall entries.  Remove the redundant headers and reduce the
others.

This patch (of 8):

Some architectures may need to override the compat sigreturn definition,
as is already possible in the non-compat case.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-generic/seccomp.h

@@ -17,7 +17,9 @@
 #define __NR_seccomp_read_32		__NR_read
 #define __NR_seccomp_write_32		__NR_write
 #define __NR_seccomp_exit_32		__NR_exit
+#ifndef __NR_seccomp_sigreturn_32
 #define __NR_seccomp_sigreturn_32	__NR_rt_sigreturn
+#endif
 #endif /* CONFIG_COMPAT && ! already defined */
 
 #define __NR_seccomp_read		__NR_read