[PATCH] make gl_VISIBILITY to reject unsupported configurations with newer gcc

[Ozkan Sezer]

The attached patch makes gl_VISIBILITY to reject unsupported configurations
with newer gcc: In its current form, mingw gcc-4.5.4 rejects the attributes
but gcc-7.5 does not, apparently because the attributes are applied to func
prototypes without their definitions.  Attaching a hidden visibility attrib
to dummyfunc() makes gcc-7.5 to reject it properly.

--
O.S.

From 1c7e9ca1f5ad6f2b7dcd65f0bdfefec16ff6ad06 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <seze...@gmail.com>
Date: Tue, 25 May 2021 18:47:14 +0300
Subject: [PATCH] m4/visibility.m4 (gl_VISIBILITY): properly reject unsupported configurations with newer gcc

---
 m4/visibility.m4 |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/m4/visibility.m4 b/m4/visibility.m4
index 8f27a12..91970a9 100644
--- a/m4/visibility.m4
+++ b/m4/visibility.m4
@@ -1,4 +1,4 @@
-# visibility.m4 serial 7
+# visibility.m4 serial 8
 dnl Copyright (C) 2005, 2008, 2010-2021 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -58,7 +58,7 @@ AC_DEFUN([gl_VISIBILITY],
               extern __attribute__((__visibility__("default"))) int exportedvar;
               extern __attribute__((__visibility__("hidden"))) int hiddenfunc (void);
               extern __attribute__((__visibility__("default"))) int exportedfunc (void);
-              void dummyfunc (void);
+              extern __attribute__((__visibility__("hidden"))) void dummyfunc (void);
               void dummyfunc (void) {}
             ]],
             [[]])],
-- 
1.7.1