i#3956 arm locks: Use release-acquire atomics for ARM (#4262)
i#3956 arm locks: Use release-acquire atomics for ARM (#4262)

Adds a "dmb ish" barrier prior to the "ldrex..strex" loops in the
atomics used to implement mutexes and other operations on 32-bit ARM
where we need release-acquire semantics.

Issue: #3956
AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio