sem_open() is not implemented as well. Here is a gdb session with a breakpoint set at semlock_new() (SEM_FAILED is NULL on android):

Breakpoint 1, semlock_new (type=0xb6d070c0 <_PyMp_SemLockType>, 
    args=(1, 1, 1, '/mp-dkzrq4ed', True), kwds=0x0)
    at /home/xavier/src/packages/android/cpython/Modules/_multiprocessing/semaphore.c:420
420     {
(gdb) next
428         if (!PyArg_ParseTupleAndKeywords(args, kwds, "iiisi", kwlist,
(gdb) 
432         if (kind != RECURSIVE_MUTEX && kind != SEMAPHORE) {
(gdb) 
437         if (!unlink) {
(gdb) 
424         char *name, *name_copy = NULL;
(gdb) 
445         handle = SEM_CREATE(name, value, maxvalue);
(gdb) 
447         if (handle == SEM_FAILED || SEM_GET_LAST_ERROR() != 0)
(gdb) print handle
$5 = (SEM_HANDLE) 0x0
(gdb) next
460         if (handle != SEM_FAILED)
(gdb) 
462         PyMem_Free(name_copy);
(gdb) 
463         _PyMp_SetError(NULL, MP_STANDARD_ERROR);
(gdb) 
464         return NULL;
(gdb) 


This is run with sem_unlink_alt.diff modified to include the change to 'define SEM_UNLINK(name) 0' although I guess this does not change anything.

Sorry for misleading you about sem_unlink().