Revert "libc: types: Remove wrong definition"

This reverts commit 2a63e342f40918e2920f404f4ad75b35d64c539f.

This needs to be reverted as otherwise the type of ssize_t will be
"unsigned long" which is not correct.

    (gdb) ptype ssize_t
    type = unsigned long

For example this check would fail in that case

    ssize_t foo(void)
    {
        return -1;
    }
    ...
    if (foo() < 0) {
        printk("This is never called\n");
    }

Fixes #17378

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>