modules example

gcc example:

```
import <iostream>;

int main()
{
    std::cout << "Hello modules!\n";
    return 0;
}
```

https://i.imgur.com/Y0gR8p7.png

g++ -std=c++20 -fmodules-ts -x c++-system-header iostream

g++ -std=c++20 -fmodules-ts main.cpp -o hello

clang++ -std=c++20 -stdlib=libc++ -fmodules -fbuiltin-module-map main.cpp -o hello


Here steps with MSVC:

1. Install 16.10 Preview 2

2. enter some code with header units.

My example:
```
import <iostream>;
import <vector>;

int main()
{
    std::vector v{1,2,3};
    std::cout << "Hello modules!\n";
    return static_cast<int>(v.size());
}
```

3. Open command promt for Visual Studio 2019 Preview.

4. Compile header units which you use.

for iostream:

cl /EHsc /nologo /W4 /std:c++latest /MD  /exportHeader /headerName:angle iostream /Fo:iostream.obj

for vector:

cl /EHsc /nologo /W4 /std:c++latest /MD  /exportHeader /headerName:angle vector /Fo:vector.obj

5. Compile example:

cl /EHsc /nologo /W4 /std:c++latest /MD /headerUnit:angle "iostream=iostream.ifc" /headerUnit:angle "vector=vector.ifc" main.cpp iostream.obj vector.obj
main.cpp

Real screenshot:

https://i.imgur.com/WElKYjo.png