fix(compilation): Include stdint.h for SIZE_MAX on Linux

Signed-off-by: George Boumis <developer.george.boumis@gmail.com>
chore(retainCount): Add volatile attribute

Use volatile to be sure that compiler does not optimize away memory
accesses. Usefull when there are setjmp(3)s and longjmp(3)s in the way.

Signed-off-by: George Boumis <developer.george.boumis@gmail.com>