sparc: Simplify <asm/siginfo.h>

There is no need for the forward declaration of compat_siginfo provided
here.  We can't yet use the generic header as we need to pull in the
sparc-specific version of the uapi <asm/siginfo.h>, but this prepares
for removing the non-uapi <asm/siginfo.h> entirely.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-ia64@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/20170603190102.28866-2-hch@lst.de

arch/sparc/include/asm/siginfo.h

-#ifndef __SPARC_SIGINFO_H
-#define __SPARC_SIGINFO_H
-
 #include <uapi/asm/siginfo.h>
-
-
-#ifdef CONFIG_COMPAT
-
-struct compat_siginfo;
-
-#endif /* CONFIG_COMPAT */
-
-#endif /* !(__SPARC_SIGINFO_H) */