Do we really need g++ option in Kconfig for nemu?

```
menu "Build Options"
choice
  prompt "Compiler"
  default CC_GCC
config CC_GCC
  bool "gcc"
config CC_GPP
  bool "g++"
config CC_CLANG
  depends on !TARGET_AM
  bool "clang"
endchoice
```

When switch from gcc to g++, build process failed due to some type conversion issues, I'm thinking If we can drop this option, or fix those  issues?