bst_vs_heap_vs_hashmap: create nicer version with separated benchmarks

One data structure per executable, and gem5 instrumented versions in
separate executables.

Create the allowed_emulators path_properties property.

TODO: wire it up to benchmark result generation and remove the old version.

userland/algorithm/set/std_unordered_set_gem5.cpp

@@ -0,0 +1,3 @@
+#define LKMC_M5OPS_ENABLE 1
+#define LKMC_ALGORITHM_SET_STD_UNORDERED_SET 1
+#include "main.hpp"