Docker + ubuntu image 编译 emsdk 失败，提示 No CMAKE_CXX_COMPILER could be found

镜像 ubuntu:latest

环境准备, [参考](http://webassembly.org/getting-started/developers-guide/)

```shell
$ apt update
$ apt install git cmake gcc python
```

编译
```shell
$ git clone https://github.com/juj/emsdk.git
$ cd emsdk
$ ./emsdk install sdk-incoming-64bit binaryen-master-64bit
```

报错
```shell
CMake Error at CMakeLists.txt:47 (project): No CMAKE_CXX_COMPILER could be found. Tell CMake where to find the compiler by setting either the environment variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path to the compiler, or to the compiler name if it is in the PATH. -- Configuring incomplete, errors occurred! See also "/root/emsdk/clang/fastcomp/build_incoming_64/CMakeFiles/CMakeOutput.log". See also "/root/emsdk/clang/fastcomp/build_incoming_64/CMakeFiles/CMakeError.log". CMake invocation failed due to exception! Working directory: /root/emsdk/clang/fastcomp/build_incoming_64 Command '['cmake', '-G', 'Unix Makefiles', '-DCMAKE_BUILD_TYPE=RelWithDebInfo', '-DPYTHON_EXECUTABLE=/usr/bin/python', '-DLLVM_TARGETS_TO_BUILD=X86;JSBackend', '-DLLVM_INCLUDE_EXAMPLES=OFF', '-DCLANG_INCLUDE_EXAMPLES=OFF', '-DLLVM_INCLUDE_TESTS=OFF', '-DCLANG_INCLUDE_TESTS=OFF', '-DLLVM_ENABLE_ASSERTIONS=ON', '/root/emsdk/clang/fastcomp/src']' returned non-zero exit status 1 Installation failed!
```

解决

官方的[入门指南](http://webassembly.org/getting-started/developers-guide/)里只提到gcc，但实际也依赖 g++。一步到位可以安装 `build-essential`，想要精简可以只安装 `cmake` `gcc` 和 `g++`

所以，**安装 g++** 后重新编译

```shell
$ apt install g++
```

解决。