[llvm] [SystemZ][z/OS] z/OS does not support nanosleep, use usleep instead (PR #109823)

[Zibi Sarbinowski via llvm-commits]

================
@@ -27,6 +27,10 @@ void SleepMS() {
   struct timespec Interval;
   Interval.tv_sec = 0;
   Interval.tv_nsec = 1000000;
+#if defined(__MVS__)
+  long Microseconds = (Interval.tv_nsec + 999) / 1000;
+  usleep(Microseconds);
+#else
----------------
zibi2 wrote:

```suggestion
#if defined(__MVS__)
using namespace std::__ibm;
#endif
```

https://github.com/llvm/llvm-project/pull/109823