Systemd prctl implementation

[arihant2math]

Adds stubs and implementation for:

const PR_SET_PDEATHSIG: i32 = 1;
const PR_GET_PDEATHSIG: i32 = 2;
const PR_GET_DUMPABLE: i32 = 3;
const PR_SET_DUMPABLE: i32 = 4;
const PR_SET_MM: i32 = 35;