havelib: Recognize ELF platform despite nvc 22.1

[Bruno Haible]

With nvc 22.1 on Linux, the configure test
  "checking for ELF binary format..."
reports "no". This patch fixes it.


2022-01-15  Bruno Haible  <bruno@clisp.org>

        havelib: Recognize ELF platform despite nvc 22.1.
        * m4/lib-prefix.m4 (AC_LIB_PREPARE_MULTILIB): Recognize Linux as an ELF
        platform, even with a compiler that does not define __ELF__.

diff --git a/m4/lib-prefix.m4 b/m4/lib-prefix.m4
index 75071e9a96..999f712f5a 100644
--- a/m4/lib-prefix.m4
+++ b/m4/lib-prefix.m4
@@ -1,4 +1,4 @@
-# lib-prefix.m4 serial 19
+# lib-prefix.m4 serial 20
 dnl Copyright (C) 2001-2005, 2008-2022 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],
-       [#ifdef __ELF__
+       [#if defined __ELF__ || (defined __linux__ && defined __EDG__)
         Extensible Linking Format
         #endif
        ],