libbinder: O_CLOFORK

You can't use binder after forking, so we can drop the FD. The binder
driver doesn't support this (once the FD is open, we would need to
open a new context in the child process). So, the userspace API would
need to handle resetting all state. However, in general, handling this
for multi-threaded processes (because of needing to take all locks by
all libraries used by all threads and restoring state, etc...) is too
complicated to make work in Android.

Bug: 232904068
Test: binderLibTest
Change-Id: I38c354af2c69804a40dc2774086a9ab77d158ede