Fix distinction of 32-bit/64-bit mode with xlc 13.1.3 on AIX. * m4/host-cpu-c-abi.m4 (gl_HOST_CPU_C_ABI, gl_HOST_CPU_C_ABI_32BIT): Test __LP64__ instead of _ARCH_PPC64. * m4/lib-ld.m4 (AC_LIB_PROG_LD): Likewise. * lib/stddef.in.h: Likewise.