sanitize rt_sigaction() situation a bit

Switch from __ARCH_WANT_SYS_RT_SIGACTION to opposite
(!CONFIG_ODD_RT_SIGACTION); the only two architectures that
need it are alpha and sparc.  The reason for use of CONFIG_...
instead of __ARCH_... is that it's needed only kernel-side
and doing it that way avoids a mess with include order on many
architectures.

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

include/asm-generic/syscalls.h

@@ -36,9 +36,4 @@ asmlinkage long sys_rt_sigreturn(struct pt_regs *regs);
 asmlinkage long sys_rt_sigsuspend(sigset_t __user *unewset, size_t sigsetsize);
 #endif
 
-#ifndef sys_rt_sigaction
-asmlinkage long sys_rt_sigaction(int sig, const struct sigaction __user *act,
-			 struct sigaction __user *oact, size_t sigsetsize);
-#endif
-
 #endif /* __ASM_GENERIC_SYSCALLS_H */