From 8087f603ad42c15a1dd83eda1e4e077024fc8f44 Mon Sep 17 00:00:00 2001
From: Fabian Homborg <FHomborg@gmail.com>
Date: Wed, 16 Dec 2020 17:06:48 +0100
Subject: [PATCH] Stub out __has_attribute if not defined

Otherwise compilers that don't even have __has_attribute fail.

Fixes #7554
---
 config_cmake.h.in | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/config_cmake.h.in b/config_cmake.h.in
index 2a8532d2f..4dbf7520e 100644
--- a/config_cmake.h.in
+++ b/config_cmake.h.in
@@ -181,7 +181,13 @@
 
 /* Like __warn_unused, but applies to a type.
    At the moment only clang supports this as a type attribute.
+
+   We need to check for __has_attribute being a thing before or old gcc fails - #7554.
 */
+#ifndef __has_attribute
+  #define __has_attribute(x) 0  // Compatibility with non-clang and old gcc compilers.
+#endif
+
 #if defined(__clang__) && __has_attribute(warn_unused_result)
 #ifndef __warn_unused_type
 #define __warn_unused_type __attribute__ ((warn_unused_result))