MS ABI: Just use getTypeInfoInChars to get the field size

This was changed to use manual desugaring and multiplication in r201832
and fixed for multi-dimensional arrays in r201917.  However, it breaks
down in the presence of typedefs.  Rather than attempting to handle all
the desugaring, just go back to calling the generic type info code.

This was discovered while compiling SIInstrWaits.cpp in the R600
backend.