Import SIMD feature and add some workload samples (#438)

samples/workload/meshoptimizer/README.md

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+"codecbench of meshoptimizer" sample introduction
+==============
+
+This sample demonstrates how to build [codecbench of messoptimizer](https://github.com/zeux/meshoptimizer) into
+WebAssembly with simd support and run it with iwasm.
+
+## Preparation
+
+please refer to [installation instructions](../README.md).
+
+## Build with clang-11 and wasi-sdk
+
+``` shell
+$ mkdir build && cd build
+$ cmake ..
+$ make
+# to verify
+$ ls codecbench.wasm
+```
+
+## Or build with EMCC
+
+EMCC is another toolchain to compile C code to WASM. In this case, will have
+a higher performance with EMCC.
+
+``` shell
+$ git clone https://github.com/zeux/meshoptimizer.git
+$ cd messoptimizer
+$ emcc tools/codecbench.cpp src/vertexcodec.cpp src/vertexfilter.cpp \
+       src/overdrawanalyzer.cpp src/indexgenerator.cpp src/vcacheoptimizer.cpp \
+       src/clusterizer.cpp src/indexcodec.cpp src/vfetchanalyzer.cpp \
+       src/spatialorder.cpp src/allocator.cpp src/vcacheanalyzer.cpp \
+       src/vfetchoptimizer.cpp src/overdrawoptimizer.cpp src/simplifier.cpp \
+       src/stripifier.cpp -O3 -msimd128 \
+       -s TOTAL_MEMORY=268435456 -s "EXPORTED_FUNCTIONS=['_main']" \
+       -o codecbench.wasm
+$ ls -l codecbench.wasm
+```
+
+## Run workload
+
+Firstly please build iwasm with simd support:
+
+``` shell
+$ cd <wamr dir>/product-mini/platforms/linux/
+$ mkdir build && cd build
+$ cmake .. -DWAMR_BUILD_SIMD=1
+$ make
+```
+
+Then compile wasm file to aot file and run:
+
+``` shell
+$ cd <wamr dir>/wamr-compiler/build
+$ ./wamrc --enable-simd -o codecbench.aot codecbench.wasm
+$ cd <wamr dir>/product-mini/platforms/linux/
+$ ./iwasm codecbench.aot
+```
+