Workaround gcc 10.x bug

configure.ac

 ## ExampleLib Example: an example of using Automake to link with a library
 
-AC_INIT([ED25519], [3:11], [bernd@net2o.de], [ed25519-donna],
+AC_INIT([ED25519], [3:12], [bernd@net2o.de], [ed25519-donna],
         [http://keccak.noekeon.org/])
 AC_PREREQ([2.59])
 AM_INIT_AUTOMAKE([1.10 -Wall no-define])

ed25519-donna.h

@@ -64,7 +64,7 @@ typedef unsigned char hash_512bits[64];
 /*
 	Timing safe memory compare
 */
-static inline int ed25519_verify(long* a, long* b, size_t len) {
+static inline int ed25519_verify(const long* a, const long* b, size_t len) {
   long diff=0;
   assert(len == 32);
   switch(sizeof(long)) {