[3.12] gh-89891: Refer SharedMemory implementation as POSIX (GH-104678) (GH-114873)

It only uses POSIX API.
(cherry picked from commit 500ede01178a8063bb2a3c664172dffa1b40d7c9)

Co-authored-by: Oleg Iarygin <oleg@arhadthedev.net>