havelib: Recognize ELF platform despite SunPRO C on Linux

[Bruno Haible]

Building a testdir on Linux with Oracle Developer Studio 12.6 (which includes 
the SunPRO C compiler), I see this configure finding:

checking for ELF binary format... no

This patch fixes it.


2024-03-28  Bruno Haible  <bruno@clisp.org>

        havelib: Recognize ELF platform despite SunPRO C on Linux.
        * m4/lib-prefix.m4 (AC_LIB_PREPARE_MULTILIB): Recognize Linux as an ELF
        platform, even with the SunPRO C compiler that does not define __ELF__.

diff --git a/m4/lib-prefix.m4 b/m4/lib-prefix.m4
index f327c6ef03..61dc248e3d 100644
--- a/m4/lib-prefix.m4
+++ b/m4/lib-prefix.m4
@@ -1,4 +1,4 @@
-# lib-prefix.m4 serial 22
+# lib-prefix.m4 serial 23
 dnl Copyright (C) 2001-2005, 2008-2024 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -174,7 +174,7 @@ AC_DEFUN([AC_LIB_PREPARE_MULTILIB]
 
   AC_CACHE_CHECK([for ELF binary format], [gl_cv_elf],
     [AC_EGREP_CPP([Extensible Linking Format],
-       [#if defined __ELF__ || (defined __linux__ && defined __EDG__)
+       [#if defined __ELF__ || (defined __linux__ && (defined __EDG__ || 
defined __SUNPRO_C))
         Extensible Linking Format
         #endif
        ],