Saved the answer of the post from https://stackoverflow.com/questions/26185978/macos-wchar-h-file-not-found
First ensure that the latest XCode is installed. Next, we need to install/fix/update Command Line Tools. To do so, run
$ xcode-select --install
Previously, XCode expected it's active developer directory to be located at
/Applications/Xcode.app/Contents/Developer/
but the latest Command Line Tools is installed to
/Library/Developer/CommandLineTools/
so we need to switch where XCode is looking. To do so, run
sudo xcode-select --switch /Library/Developer/CommandLineTools/