this works by building a directed graph of acquired
pthread mutexes and making sure there are no loops in
that graph.
this feature is enabled with:
setprop debug.libc.pthread 1
when a potential deadlock is detected, a large warning is
output to the log with appropriate back traces.
currently disabled at compile-time. set PTHREAD_DEBUG_ENABLED=1
to enable.
Change-Id: I916eed2319599e8aaf8f229d3f18a8ddbec3aa8a
