Revert "[test] Address TestConcurrentMany*.py flakiness on macOS"

This reverts my change to pseudo_barrier.h which isn't necessary anymore
after Fred's fix to debugserver and caused TestThreadStepOut to fail.

llvm-svn: 370963
(cherry picked from commit 85d6edb)

Author: JDevlieghere

lldb/packages/Python/lldbsuite/test/make/pseudo_barrier.h

@@ -1,14 +1,21 @@
 #include <atomic>
-#include <thread>
+
+// Note that although hogging the CPU while waiting for a variable to change
+// would be terrible in production code, it's great for testing since it avoids
+// a lot of messy context switching to get multiple threads synchronized.
 
 typedef std::atomic<int> pseudo_barrier_t;
 
-static inline void pseudo_barrier_wait(pseudo_barrier_t &barrier) {
-  --barrier;
-  while (barrier > 0)
-    std::this_thread::yield();
-}
+#define pseudo_barrier_wait(barrier)        \
+    do                                      \
+    {                                       \
+        --(barrier);                        \
+        while ((barrier).load() > 0)        \
+            ;                               \
+    } while (0)
 
-static inline void pseudo_barrier_init(pseudo_barrier_t &barrier, int count) {
-  barrier = count;
-}
+#define pseudo_barrier_init(barrier, count) \
+    do                                      \
+    {                                       \
+        (barrier) = (count);                \
+    } while (0)