Determine `long long` availability based on its size.

MSVC, for example, used `long long` even without full C99 support.

* include/freetype/config/ftstdlib.h: Check if `long long` limits are
defined in <limits.h>.
* include/freetype/config/integer-types.h: Check `long long` size and
use it to typedef FT_Int64.
2 files changed