Use __has_extension and __has_feature is a way compatible with old gcc
diff --git a/src/pthreadpool.c b/src/pthreadpool.c
index 5eb7972..e9dbd18 100644
--- a/src/pthreadpool.c
+++ b/src/pthreadpool.c
@@ -15,12 +15,16 @@
#define PTHREADPOOL_CACHELINE_SIZE 64
#define PTHREADPOOL_CACHELINE_ALIGNED __attribute__((__aligned__(PTHREADPOOL_CACHELINE_SIZE)))
-#if (defined(__clang__) && (__has_extension(c_static_assert) || __has_feature(c_static_assert))) || \
- (defined(__GNUC__) && ((__GNUC__ > 4) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 6)))
- /* Static assert is supported by gcc >= 4.6 and modern clang */
+#if defined(__clang__)
+ #if __has_extension(c_static_assert) || __has_feature(c_static_assert)
+ #define PTHREADPOOL_STATIC_ASSERT(predicate, message) _Static_assert((predicate), message)
+ #else
+ #define PTHREADPOOL_STATIC_ASSERT(predicate, message)
+ #endif
+#elif defined(__GNUC__) && ((__GNUC__ > 4) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 6))
+ /* Static assert is supported by gcc >= 4.6 */
#define PTHREADPOOL_STATIC_ASSERT(predicate, message) _Static_assert((predicate), message)
#else
- /* Dummy declaration for legacy compilers */
#define PTHREADPOOL_STATIC_ASSERT(predicate, message)
#endif
