Use C99-style variadic macros when available.

void Curl_failf(struct SessionHandle *, const char *fmt, ...);

#if defined(CURL_DISABLE_VERBOSE_STRINGS)

#if defined(__GNUC__)

/* This style of variable argument macros is a gcc extension */

#define infof(x...) /*ignore*/

#if defined(__STDC__) && defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)

/* C99 compilers support variadic macros */

#define infof(...)

#elif defined(__GNUC__)

/* This style of variable argument macros is an old gcc extension */

#define infof(x...)

#else

/* C99 compilers could use this if we could detect them */

/*#define infof(...) */

/* Cast the args to void to make them a noop, side effects notwithstanding */

#define infof (void)

#endif