Build wamrc

Both the WASM binary file and AOT file are supported by iwasm. The wamrc AOT compiler compiles wasm binary file to AOT file, which can also be run by iwasm. Execute the following commands to build wamrc compiler for Linux:

cd wamr-compiler
./build_llvm.sh (or "./build_llvm_xtensa.sh" to support xtensa target)
mkdir build && cd build
cmake .. (or "cmake .. -DWAMR_BUILD_PLATFORM=darwin" for MacOS)
make
# wamrc is generated under current directory

For Windows：

cd wamr-compiler
python build_llvm.py
mkdir build && cd build
cmake ..
cmake --build . --config Release
# wamrc.exe is generated under .\Release directory