[lldb] Ensure that TestMemoryCache.py reads allocated memory

The test reads 400 bytes of memory above the local variable. If the
stack is shallow, this can reach non-allocated space, resulting in a
test failure.

Author: igorkudrin

lldb/test/API/functionalities/memory/cache/main.cpp

@@ -1,5 +1,11 @@
-int main ()
+int test()
 {
     int my_ints[] = {0x42};
     return 0; // Set break point at this line.
 }
+
+int main ()
+{
+    int dummy[100];
+    return test();
+}