Fix a bug in 'Remove __need macros from signal.h' (a992f506)

Fix a bug in 'Remove __need macros from signal.h' (a992f506)

siginfo-arch.h is included in two different places, so the default
definitions of the macros that it might or might not define need to
be done conditionally afterward, not unconditionally beforehand.

	* sysdeps/unix/sysv/linux/bits/siginfo-consts.h
	(__SI_ASYNCIO_AFTER_SIGIO): Define default after including
	bits/siginfo-arch.h, only if not already defined.
	* sysdeps/unix/sysv/linux/bits/types/siginfo_t.h
	(__SI_ALIGNMENT, __SI_BAND_TYPE, __SI_CLOCK_T)
	(__SI_ERRNO_THEN_CODE, __SI_HAVE_SIGSYS, __SI_SEGFAULT_ADDL):
	Likewise.

	* sysdeps/unix/sysv/linux/ia64/bits/siginfo-arch.h
	* sysdeps/unix/sysv/linux/mips/bits/siginfo-arch.h
	* sysdeps/unix/sysv/linux/sparc/bits/siginfo-arch.h
	* sysdeps/unix/sysv/linux/tile/bits/siginfo-arch.h
	* sysdeps/unix/sysv/linux/x86/bits/siginfo-arch.h:
	Unconditionally define __SI_* macros.