HPCC-11522 libmemcached plugin

Previously: #6368 & #6686

Signed-off-by: jamienoss <james.noss@lexisnexis.com>
Unfortunately has a couple of problems:
* You can't assume sizeof is 64bit.  So whenever you pass sizeof/size_t to printf you need to cast it to a fixed size type.    (It does affect the stack layout and will give you wrong values on some machines).  In this case I would cast to unsigned since they're small.

* %lu is used for a long integer.  This is different from a 64 bit integer.  Because the format specifiers for 64bit differ between windows and linux you would need to say.

...(%"I64F"u...

if the argument is 64bit.