This first prints the number into a temporary buffer and then copies the
number to the output.

A positive side effect is that cJSON no longer reserves more space for
the number in the output than is necessary.

Because sizeof('\0') is actually sizeof(int) not sizeof(char).

The compiler flag detection was working incorrectly.

This reverts commit 12acc579.

Signed-off-by: NFabrice Fontaine <fontaine.fabrice@gmail.com>

This is the first step in removing the global allocator functions. Every
internal function now only accesses its locally available set of
allocators.