Add benchmarks (#979)

Add scripts to build and run benchmark of coremark, polybench,
sightglass and jetstream2. And add documents.

tests/benchmarks/sightglass/build.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+
+# Copyright (C) 2019 Intel Corporation.  All rights reserved.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+OUT_DIR=$PWD/out
+WAMRC_CMD=$PWD/../../../wamr-compiler/build/wamrc
+SHOOTOUT_CASES="base64 fib2 gimli heapsort matrix memmove nestedloop \
+                nestedloop2 nestedloop3 random seqhash sieve strchr \
+                switch2"
+
+if [ ! -d sightglass ]; then
+    git clone https://github.com/wasm-micro-runtime/sightglass.git
+fi
+
+mkdir -p ${OUT_DIR}
+
+cd sightglass/benchmarks/shootout
+
+for bench in $SHOOTOUT_CASES
+do
+    echo "Build ${bench}_native"
+    gcc -O3 -o ${OUT_DIR}/${bench}_native -Dblack_box=set_res -Dbench=${bench} \
+        -I../../include ${bench}.c main/main_${bench}.c main/my_libc.c
+
+    echo "Build ${bench}.wasm"
+    /opt/wasi-sdk/bin/clang -O3 -nostdlib \
+        -Wno-unknown-attributes \
+        -Dblack_box=set_res \
+        -I../../include -DNOSTDLIB_MODE \
+        -Wl,--initial-memory=1310720,--allow-undefined \
+        -Wl,--strip-all,--no-entry \
+        -o ${OUT_DIR}/${bench}.wasm \
+        -Wl,--export=app_main -Wl,--export=_start \
+        ${bench}.c main/main_${bench}.c main/my_libc.c
+
+
+    echo "Compile ${bench}.wasm into ${bench}.aot"
+    ${WAMRC_CMD} -o ${OUT_DIR}/${bench}.aot ${OUT_DIR}/${bench}.wasm
+done
+
+cd ..
+
+echo "Done"