using uint128_t instead of "int128.h"

Author: dderjoel

src/third_party/secp256k1_dettman_64.h

@@ -23,9 +23,7 @@
 #  define FIAT_SECP256K1_DETTMAN_FIAT_INLINE
 #endif
 
-#include "../int128.h"
-FIAT_SECP256K1_DETTMAN_FIAT_EXTENSION typedef secp256k1_int128 fiat_secp256k1_dettman_int128;
-FIAT_SECP256K1_DETTMAN_FIAT_EXTENSION typedef secp256k1_uint128 fiat_secp256k1_dettman_uint128;
+FIAT_SECP256K1_DETTMAN_FIAT_EXTENSION typedef uint128_t fiat_secp256k1_dettman_uint128;
 
 #if (-1 & 3) != 3
 #error "This code only works on a two's complement system"