ec/native: use __extension__ keyword to allow compilation with GCC and -Wpedantic

Author: hannesm

Diff for: ec/native/np256_64.h

@@ -18,8 +18,8 @@
 #include <stdint.h>
 typedef unsigned char fiat_np256_uint1;
 typedef signed char fiat_np256_int1;
-typedef signed __int128 fiat_np256_int128;
-typedef unsigned __int128 fiat_np256_uint128;
+__extension__ typedef signed __int128 fiat_np256_int128;
+__extension__ typedef unsigned __int128 fiat_np256_uint128;
 
 #if (-1 & 3) != 3
 #error "This code only works on a two's complement system"

Diff for: ec/native/p256_64.h

@@ -18,8 +18,8 @@
 #include <stdint.h>
 typedef unsigned char fiat_p256_uint1;
 typedef signed char fiat_p256_int1;
-typedef signed __int128 fiat_p256_int128;
-typedef unsigned __int128 fiat_p256_uint128;
+__extension__ typedef signed __int128 fiat_p256_int128;
+__extension__ typedef unsigned __int128 fiat_p256_uint128;
 
 #if (-1 & 3) != 3
 #error "This code only works on a two's complement system"