Add benchmarks (#979)

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

tests/benchmarks/coremark/build.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+
+# Copyright (C) 2019 Intel Corporation.  All rights reserved.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+WAMRC="../../../wamr-compiler/build/wamrc"
+
+if [ ! -d coremark ]; then
+    git clone https://github.com/eembc/coremark.git
+fi
+
+cd coremark
+
+echo "Build coremark with gcc .."
+gcc -O3 -Iposix -I. -DFLAGS_STR=\""-O3 -DPERFORMANCE_RUN=1  -lrt"\" \
+        -DITERATIONS=0 -DPERFORMANCE_RUN=1 \
+        core_list_join.c core_main.c core_matrix.c core_state.c \
+        core_util.c posix/core_portme.c \
+        -o ../coremark.exe -lrt
+
+echo "Build coremark with wasi-sdk .."
+/opt/wasi-sdk/bin/clang -O3 -Iposix -I. -DFLAGS_STR=\""-O3 -DPERFORMANCE_RUN=1"\" \
+        -Wl,--export=main \
+        -DITERATIONS=0 -DPERFORMANCE_RUN=1 \
+        -Wl,--allow-undefined \
+        core_list_join.c core_main.c core_matrix.c core_state.c \
+        core_util.c posix/core_portme.c \
+        -o ../coremark.wasm
+
+cd ..
+
+echo "Compile coremark.wasm to coremark.aot .."
+${WAMRC} -o coremark.aot coremark.wasm
+
+echo "Done"