Merge pull request #3545 from ntherning/throw-AbandonedMutexException-on-unix

Correctly handle abandoned mutexes on non-Windows platforms

diff --cc mono/metadata/threads.c
Simple merge

diff --cc mono/metadata/w32event-unix.c
Simple merge

diff --cc mono/metadata/w32mutex-unix.c
Simple merge

diff --cc mono/metadata/w32semaphore-unix.c
Simple merge

diff --cc mono/utils/w32handle.c
Simple merge