More accurate "packed" attribute declaration.

auto/clang

@@ -146,3 +146,18 @@ nxt_feature_test="#include <stdlib.h>
                       return 0;
                   }"
 . auto/feature
+
+
+nxt_feature="GCC __attribute__ packed"
+nxt_feature_name=NXT_HAVE_GCC_ATTRIBUTE_PACKED
+nxt_feature_run=
+nxt_feature_path=
+nxt_feature_libs=
+nxt_feature_test="struct __attribute__ ((__packed__)) s {
+                      char c;
+                  };
+
+                  int main() {
+                      return 1;
+                  }"
+. auto/feature

src/nxt_clang.h

@@ -121,6 +121,17 @@ nxt_prefetch(a)
 #endif
 
 
+#if (NXT_HAVE_GCC_ATTRIBUTE_PACKED)
+
+#define nxt_packed         __attribute__((__packed__))
+
+#else
+
+#define nxt_packed
+
+#endif
+
+
 #ifndef NXT_ALIGNMENT
 
 #if (NXT_SOLARIS)
@@ -230,6 +241,4 @@ nxt_trunc_ptr(p, a)                                                           \
     (u_char *) ((uintptr_t) (p) & ~((uintptr_t) (a) - 1))
 
 
-#define NXT_PACKED  __attribute__((packed))
-
 #endif /* _NXT_CLANG_H_INCLUDED_ */