make gpr_timespec platform agnostic
diff --git a/src/core/security/credentials.c b/src/core/security/credentials.c
index 543c750..cbaec7d 100644
--- a/src/core/security/credentials.c
+++ b/src/core/security/credentials.c
@@ -511,9 +511,9 @@
       "grpc_service_account_jwt_access_credentials_create("
       "json_key=%s, "
       "token_lifetime="
-      "gpr_timespec { tv_sec: %ld, tv_nsec: %d, clock_type: %d }, "
+      "gpr_timespec { tv_sec: %lld, tv_nsec: %d, clock_type: %d }, "
       "reserved=%p)",
-      5, (json_key, (long)token_lifetime.tv_sec, token_lifetime.tv_nsec,
+      5, (json_key, (long long)token_lifetime.tv_sec, (int)token_lifetime.tv_nsec,
           (int)token_lifetime.clock_type, reserved));
   GPR_ASSERT(reserved == NULL);
   return grpc_service_account_jwt_access_credentials_create_from_auth_json_key(