Add benchmarks (#979)

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

tests/benchmarks/polybench/build.sh

@@ -0,0 +1,47 @@
+#!/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
+POLYBENCH_CASES="datamining linear-algebra medley stencils"
+
+if [ ! -d PolyBenchC-4.2.1 ]; then
+    git clone https://github.com/MatthiasJReisinger/PolyBenchC-4.2.1.git
+fi
+
+mkdir -p ${OUT_DIR}
+
+cd PolyBenchC-4.2.1
+
+for case in $POLYBENCH_CASES
+do
+    files=`find ${case} -name "*.c"`
+    for file in ${files}
+    do
+        file_name=${file##*/}
+        if [[ ${file_name} == "Nussinov.orig.c" ]]; then
+            continue
+        fi
+
+        echo "Build ${file_name%.*}_native"
+        gcc -O3 -I utilities -I ${file%/*} utilities/polybench.c ${file} \
+                -DPOLYBENCH_TIME -lm -o ${OUT_DIR}/${file_name%.*}_native
+
+        echo "Build ${file_name%.*}.wasm"
+        /opt/wasi-sdk/bin/clang -O3 -I utilities -I ${file%/*}      \
+                utilities/polybench.c ${file}                       \
+                -Wl,--export=__heap_base -Wl,--export=__data_end    \
+                -Wl,--export=malloc -Wl,--export=free               \
+                -DPOLYBENCH_TIME -o ${OUT_DIR}/${file_name%.*}.wasm
+
+        echo "Compile ${file_name%.*}.wasm into ${file_name%.*}.aot"
+        ${WAMRC_CMD} -o ${OUT_DIR}/${file_name%.*}.aot \
+                ${OUT_DIR}/${file_name%.*}.wasm
+    done
+done
+
+cd ..
+
+echo "Done"