alignof, intprops, malloca: port better to IBM's C compiler * lib/alignof.h (alignof_type) [__IBM_ALIGNOF__]: Use __alignof__. * lib/intprops.h (_GL_HAVE___TYPEOF__) [__IBM_TYPEOF__]: Now 1. * lib/malloca.h (sa_alignof): [__IBM_ALIGNOF__]: Use __alignof__.