Merge 5f62334695 into 4fe9018b6f

GCC 15 starts warning about non NUL-terminated string literals:

    chacha.c:44:31: error: initializer-string for array of ‘char’ truncates NUL terminator but destination lacks ‘nonstring’ attribute (17 chars into 16 available) [-Werror=unterminated-string-initialization]
       44 | static const char sigma[16] = "expand 32-byte k";
          |                               ^~~~~~~~~~~~~~~~~~

util.h

@@ -33,8 +33,12 @@
 #define ALIAS(f) __attribute__((alias(STRINGIFY(f))))
 
 // supported since GCC 15
-#if __has_attribute (nonstring)
+#if defined __has_attribute
+#  if __has_attribute (nonstring)
 #    define NONSTRING __attribute__ ((nonstring))
+#  else
+#    define NONSTRING
+#  endif
 #else
 #  define NONSTRING
 #endif