rocr: Temporarily disable alternate scratch memory

Temporarily disable alternate scratch memory usage by default due to
some stability issues.

runtime/hsa-runtime/core/util/flag.h

@@ -154,7 +154,9 @@ class Flag {
     enable_scratch_async_reclaim_ = (var == "0") ? false : true;
 
     var = os::GetEnvVar("HSA_ENABLE_SCRATCH_ALT");
-    enable_scratch_alt_ = (var == "0") || !enable_scratch_async_reclaim_ ? false : true;
+    //Temporary: Disable alternate scratch by default as it can cause occasional hangs
+    //enable_scratch_alt_ = (var == "0") || !enable_scratch_async_reclaim_ ? false : true;
+    enable_scratch_alt_ = (var == "1") && enable_scratch_async_reclaim_ ? true : false;
 
     tools_lib_names_ = os::GetEnvVar("HSA_TOOLS_LIB");