consolidate kernel-side struct sigaction declarations

arch/alpha/include/asm/signal.h

arch/arm/include/asm/signal.h

arch/avr32/include/asm/signal.h

arch/cris/include/asm/signal.h

arch/h8300/include/asm/signal.h

arch/ia64/include/asm/signal.h

arch/ia64/include/asm/unistd.h

arch/m32r/include/asm/signal.h

arch/m68k/include/asm/signal.h

arch/mips/include/asm/signal.h

arch/mips/include/uapi/asm/signal.h

arch/mn10300/include/asm/signal.h

arch/parisc/include/asm/signal.h

arch/powerpc/include/asm/signal.h

arch/powerpc/include/asm/syscalls.h

arch/powerpc/include/uapi/asm/signal.h

arch/s390/include/asm/signal.h

arch/sparc/include/asm/signal.h

arch/sparc/include/uapi/asm/signal.h

arch/sparc/kernel/systbls.h