sparc: switch sys_compat_rt_sigaction() to COMPAT_SYSCALL_DEFINE

note that while struct compat_sigaction is the generic one, syscall
itself *isn't* - different arguments.  IOW, CONFIG_ODD_RT_SIGACTION
stays.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/sparc/Kconfig

@@ -46,6 +46,7 @@ config SPARC
 	select GENERIC_COMPAT_RT_SIGQUEUEINFO
 	select GENERIC_COMPAT_RT_SIGPROCMASK
 	select GENERIC_COMPAT_RT_SIGPENDING
+	select GENERIC_COMPAT_RT_SIGACTION
 
 config SPARC32
 	def_bool !64BIT