Fix distinction of 32-bit/64-bit mode with xlc 13.1.3 on AIX

[Bruno Haible]

Starting with xlc version 13, this compiler defines the preprocessor macro
_ARCH_PPC64 also in 32-bit builds. See:

$ xlc -qversion
IBM XL C/C++ for AIX, V12.1 (5765-J02, 5725-C72)
Version: 12.01.0000.0000
$ echo > empty.c ; xlc -qshowmacros=pre -E empty.c | grep ARCH_PPC
#define _ARCH_PPC 1

$ xlc -qversion
IBM XL C/C++ for AIX, V13.1.3 (5725-C72, 5765-J07)
Version: 13.01.0003.0006
$ echo > empty.c ; xlc -qshowmacros=pre -E empty.c | grep ARCH_PPC
#define _ARCH_PPCGR 1
#define _ARCH_PPC64GRSQ 1
#define _ARCH_PPC 1
#define _ARCH_PPC64GR 1
#define _ARCH_PPC64 1

So, in order to distinguish a 32-bit mode from a 64-bit mode, only the
following macros can be used:
  - defined in 32-bit mode only: _ILP32 __ILP32__
  - defined in 64-bit mode only: _LP64 __LP64__ __64BIT__

This patch fixes it.


2021-02-14  Bruno Haible  <bruno@clisp.org>

        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.

diff --git a/lib/stddef.in.h b/lib/stddef.in.h
index 6385892..ba6f903 100644
--- a/lib/stddef.in.h
+++ b/lib/stddef.in.h
@@ -51,7 +51,7 @@
 
 /* On AIX 7.2, with xlc in 64-bit mode, <stddef.h> defines max_align_t to a
    type with alignment 4, but 'long' has alignment 8.  */
-#  if defined _AIX && defined _ARCH_PPC64
+#  if defined _AIX && defined __LP64__
 #   if !GNULIB_defined_max_align_t
 #    ifdef _MAX_ALIGN_T
 /* /usr/include/stddef.h has already defined max_align_t.  Override it.  */
diff --git a/m4/host-cpu-c-abi.m4 b/m4/host-cpu-c-abi.m4
index 7dc830e..64e28b1 100644
--- a/m4/host-cpu-c-abi.m4
+++ b/m4/host-cpu-c-abi.m4
@@ -1,4 +1,4 @@
-# host-cpu-c-abi.m4 serial 13
+# host-cpu-c-abi.m4 serial 14
 dnl Copyright (C) 2002-2021 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -211,7 +211,7 @@ changequote([,])dnl
          # be generating 64-bit code.
          AC_COMPILE_IFELSE(
            [AC_LANG_SOURCE(
-              [[#if defined __powerpc64__ || defined _ARCH_PPC64
+              [[#if defined __powerpc64__ || defined __LP64__
                  int ok;
                 #else
                  error fail
@@ -605,7 +605,7 @@ changequote([,])dnl
            # be generating 64-bit code.
            AC_COMPILE_IFELSE(
              [AC_LANG_SOURCE(
-                [[#if defined __powerpc64__ || defined _ARCH_PPC64
+                [[#if defined __powerpc64__ || defined __LP64__
                    int ok;
                   #else
                    error fail
diff --git a/m4/lib-ld.m4 b/m4/lib-ld.m4
index aa07cb4..076358d 100644
--- a/m4/lib-ld.m4
+++ b/m4/lib-ld.m4
@@ -1,4 +1,4 @@
-# lib-ld.m4 serial 9
+# lib-ld.m4 serial 10
 dnl Copyright (C) 1996-2003, 2009-2021 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -122,7 +122,7 @@ else
       *-*-aix*)
         AC_COMPILE_IFELSE(
           [AC_LANG_SOURCE(
-             [[#if defined __powerpc64__ || defined _ARCH_PPC64
+             [[#if defined __powerpc64__ || defined __LP64__
                 int ok;
                #else
                 error fail