Command line tools are not working in xcode 10.2 update

I'm running Mojave 10.14.4. I just updated Xcode to 10.2. I installed command line tools via Software Update.

I have this C++ program:

#include 

int
main()
{
    std::cout << "Hello World\n";
}

I try to compile it with this command:

clang++ test.cpp

The result is:

In file included from test.cpp:1:

In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/iostream:38:

In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/ios:215:

In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/iosfwd:90:

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/wchar.h:119:15: fatal error:

'wchar.h' file not found

#include_next <wchar.h>

^~~~~~~~~

1 error generated.

How do I repair my command line development environment?

Thanks.