Added script to run benches with PGO

scripts/pgo.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+default_host_triple=""
+default_toolchain=""
+IFS=" = "
+while read -r name value
+do
+  value="${value//\"/}"
+  if [ "${name}" == "default_host_triple" ]; then
+    default_host_triple="${value}"
+  elif [ "${name}" == "default_toolchain" ]; then
+    default_toolchain="${value}"
+  fi
+done < ~/.rustup/settings.toml
+
+echo "default_host_triple=${default_host_triple}"
+echo "default_toolchain=${default_toolchain}"
+
+rustup component add llvm-tools-preview
+
+rm -rf /tmp/merk-pgo
+RUSTFLAGS="-Cprofile-generate=/tmp/merk-pgo" cargo bench rand_rocks
+~/.rustup/toolchains/${default_toolchain}/lib/rustlib/${default_host_triple}/bin/llvm-profdata merge -o /tmp/merk-pgo/merged.profdata /tmp/merk-pgo
+RUSTFLAGS="-Cprofile-use=/tmp/merk-pgo/merged.profdata" cargo bench