[Orc] Disable use of shared memory on Android

shm_open and shm_unlink are not available on Android. This commit
disables SharedMemoryMapper on Android until a better solution is
available.

https://android.googlesource.com/platform/bionic/+/refs/heads/master/docs/status.md
https://github.com/llvm/llvm-project/issues/56812

Differential Revision: https://reviews.llvm.org/D130814