8013057: assert(_needs_gc || SafepointSynchronize::is_at_safepoint()) failed: only read at safepoint Summary: Detect mmap() commit failures in Linux and Solaris os::commit_memory() impls and call vm_exit_out_of_memory(). Add os::commit_memory_or_exit(). Also tidy up some NMT accounting and some mmap() return value checking. Reviewed-by: zgu, stefank, dholmes, dsamersoff