Add lifetimebound to attributes for general-purpose usage

Co-authored-by: practicalswift <practicalswift@users.noreply.github.com>

src/attributes.h

@@ -19,4 +19,14 @@
 #  endif
 #endif
 
+#if defined(__clang__)
+#  if __has_attribute(lifetimebound)
+#    define LIFETIMEBOUND [[clang::lifetimebound]]
+#  else
+#    define LIFETIMEBOUND
+#  endif
+#else
+#  define LIFETIMEBOUND
+#endif
+
 #endif // BITCOIN_ATTRIBUTES_H