Further testing suggested one more patch (attached), which I also installed into
Gnulib master on savannah.
>From 05b2d40dd751dd182f58118f4d3273ad8136b4ee Mon Sep 17 00:00:00 2001
From: Paul Eggert <egg...@cs.ucla.edu>
Date: Sun, 4 Oct 2020 18:12:50 -0700
Subject: [PATCH] c-stack: pacify GCC 9.3.1 when using libsigsegv
* lib/c-stack.c [USE_LIBSIGSEGV]: Disable --suggest-attribute=pure.
---
ChangeLog | 5 +++++
lib/c-stack.c | 5 +++++
2 files changed, 10 insertions(+)
diff --git a/ChangeLog b/ChangeLog
index 83b92302d..e0c821f7d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2020-10-04 Paul Eggert <egg...@cs.ucla.edu>
+
+ c-stack: pacify GCC 9.3.1 when using libsigsegv
+ * lib/c-stack.c [USE_LIBSIGSEGV]: Disable --suggest-attribute=pure.
+
2020-10-04 Bruno Haible <br...@clisp.org>
localename: Fix a couple of "unused parameter" warnings.
diff --git a/lib/c-stack.c b/lib/c-stack.c
index 187bcafff..3aea16acd 100644
--- a/lib/c-stack.c
+++ b/lib/c-stack.c
@@ -168,6 +168,11 @@ null_action (int signo _GL_UNUSED)
#if USE_LIBSIGSEGV
+/* Pacify GCC 9.3.1, which otherwise would complain about segv_handler. */
+# if __GNUC_PREREQ (4, 6)
+# pragma GCC diagnostic ignored "-Wsuggest-attribute=pure"
+# endif
+
/* Nonzero if general segv handler could not be installed. */
static volatile int segv_handler_missing;
--
2.25.1
