On Windows, wildcard expansion isn't performed by the shell, but left to the program itself. The common way to do this is to link with setargv.obj, which performs the expansion on argc/argv before main is entered. However, we don't use argv in Clang on Windows, but instead call GetCommandLineW so we can handle unicode arguments. This means we have to do wildcard expansion ourselves.
Here is a stab at making GetArgumentVector perform wildcard expansion. I'm very open for ideas on how to test this, and also if this is the right place for the code to live.