Improve wur coverage on older GCCs

* src/conf_post.h (__has_attribute_warn_unused_result):
New macro for compilers lacking __has_attribute.
* src/systhread.h (__has_attribute): Remove ineffective define.
(ATTRIBUTE_WARN_UNUSED_RESULT): Work better on GCC 3.4 thru 4.

2 files changed, 3 insertions, 6 deletions

diff --git a/src/conf_post.h b/src/conf_post.h
index 6ea2c7b664b..7699d2c95bc 100644
--- a/src/conf_post.h
+++ b/src/conf_post.h
@@ -78,6 +78,7 @@ typedef bool bool_bf;
 # define __has_attribute_no_address_safety_analysis false
 # define __has_attribute_no_sanitize_address GNUC_PREREQ (4, 8, 0)
 # define __has_attribute_no_sanitize_undefined GNUC_PREREQ (4, 9, 0)
+# define __has_attribute_warn_unused_result GNUC_PREREQ (3, 4, 0)
 #endif
 
 /* Simulate __has_feature on compilers that lack it.  It is used only
diff --git a/src/systhread.h b/src/systhread.h
index a1d2746721d..8070bcde752 100644
--- a/src/systhread.h
+++ b/src/systhread.h
@@ -21,12 +21,8 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 #include <stdbool.h>
 
-#ifndef __has_attribute
-# define __has_attribute(a) false
-#endif
-
-#if __has_attribute (__warn_unused_result__)
-# define ATTRIBUTE_WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
+#if __has_attribute (warn_unused_result)
+# define ATTRIBUTE_WARN_UNUSED_RESULT __attribute__ ((warn_unused_result))
 #else
 # define ATTRIBUTE_WARN_UNUSED_RESULT
 #endif