sigsegv: Clarify license of the *.m4 files

[Bruno Haible]

Two *.m4 files, copied from GNU libsigsegv, only state "GPL" without
stating the version of the GPL. Before 2007, this was obvious. Since 2007,
it matters.

This patch clarifies it.


2024-08-30  Bruno Haible  <bruno@clisp.org>

        sigsegv: Clarify license of the *.m4 files.
        * m4/sigaltstack.m4: In the license notice, clarify which version of the
        GPL is meant.
        * m4/stack-direction.m4: Likewise.

diff --git a/m4/sigaltstack.m4 b/m4/sigaltstack.m4
index 3dcfe60aea..a710642493 100644
--- a/m4/sigaltstack.m4
+++ b/m4/sigaltstack.m4
@@ -1,11 +1,13 @@
 # sigaltstack.m4
-# serial 15
+# serial 16
 dnl Copyright (C) 2002-2024 Free Software Foundation, Inc.
 dnl This file is free software, distributed under the terms of the GNU
-dnl General Public License.  As a special exception to the GNU General
-dnl Public License, this file may be distributed as part of a program
-dnl that contains a configuration script generated by Autoconf, under
-dnl the same distribution terms as the rest of that program.
+dnl General Public License as published by the Free Software Foundation;
+dnl either version 2 of the License, or (at your option) any later version.
+dnl As a special exception to the GNU General Public License, this file
+dnl may be distributed as part of a program that contains a configuration
+dnl script generated by Autoconf, under the same distribution terms as
+dnl the rest of that program.
 
 dnl Written by Bruno Haible and Eric Blake.
 
diff --git a/m4/stack-direction.m4 b/m4/stack-direction.m4
index 1618075132..65718def65 100644
--- a/m4/stack-direction.m4
+++ b/m4/stack-direction.m4
@@ -1,11 +1,13 @@
 # stack-direction.m4
-# serial 11
+# serial 12
 dnl Copyright (C) 2002-2024 Free Software Foundation, Inc.
 dnl This file is free software, distributed under the terms of the GNU
-dnl General Public License.  As a special exception to the GNU General
-dnl Public License, this file may be distributed as part of a program
-dnl that contains a configuration script generated by Autoconf, under
-dnl the same distribution terms as the rest of that program.
+dnl General Public License as published by the Free Software Foundation;
+dnl either version 2 of the License, or (at your option) any later version.
+dnl As a special exception to the GNU General Public License, this file
+dnl may be distributed as part of a program that contains a configuration
+dnl script generated by Autoconf, under the same distribution terms as
+dnl the rest of that program.
 
 dnl Written by Bruno Haible.