brief explanation

include/PR/os_internal_rsp.h

@@ -1,4 +1,3 @@
-
 #ifndef PR_OS_INTERNAL_RSP_H
 #define PR_OS_INTERNAL_RSP_H
 

include/attributes.h

@@ -1,10 +1,15 @@
 #ifndef ATTRIBUTES_H
 #define ATTRIBUTES_H
 
+// If not building with a modern GCC-like compiler then make any use of __attribute__ a no-op
 #if (!defined(__GNUC__) && !defined(__clang__)) || defined(M2CTX) || defined(__sgi)
     #ifndef __attribute__
         #define __attribute__(x)
     #endif
 #endif
 
+#define UNUSED      __attribute__((unused))
+#define FALLTHROUGH __attribute__((fallthrough))
+#define NORETURN    __attribute__((noreturn))
+
 #endif