The snprintf function is part of the C99 standard and newer systems in
most cases all support it as defined in the standard. However, some old
Windows and HP-UX systems the function behaves differently. These checks
were also removed and PHP now uses a replacement for the snprintf
function. With gradual transition to C99 usage as a minimum requirement,
it will also be able to be replaced to system's snprintf function
directly.
Additionally in this context the unused HAVE_VSNPRINTF and check for
vsnprintf have been removed. PHP uses its own vsnprintf implementation
for now until more reliable C99 compliant function can be used from the
C libraries.