Platforms that lack autotools support should define HAVE_VARIADIC_MACROS_C99

and/or HAVE_VARIADIC_MACROS_GCC for specific compiler versions that support
variadic macros with C99 style and/or old gcc style in their specific config.h
file.

If previous definitions are not done, even when aplicable, and --disable-verbose
is used, the fallback (void) method will be used to define infof, avoiding the
inclusion of unwanted strings in the resulting library/executable.