[sysprof] util: add full memory barrier fallback

[Christian Hergert <chergert src gnome org>]

commit 1c1ef02b3dfb227b0b9065e6df5fe483a17bf622
Author: Christian Hergert <chergert redhat com>
Date:   Tue Aug 23 10:08:37 2016 -0700

    util: add full memory barrier fallback

 lib/util/util.h |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/lib/util/util.h b/lib/util/util.h
index 6062d43..7c19c32 100644
--- a/lib/util/util.h
+++ b/lib/util/util.h
@@ -33,4 +33,12 @@
 #define read_barrier()           asm volatile("dsb" ::: "memory")
 #endif
 
+/*
+ * Fallback to a full memory barrier if the architecture is not yet
+ * supported with a lighter read barrier.
+ */
+#ifndef read_barrier
+#define read_barrier()           __sync_synchronize()
+#endif
+
 #endif /* SP_UTIL_H */