GetDefaultPrinterA/W() is included in winspool.lib, but with the same attributes as in M$ import libs. For some reason the import is by ordinal, although it looks like the export is by name (GetProcAddress by name works). No idea why. Using M$ tools and SDK gives the same linker error.
Use GetProcAddress(..., "GetDefaultPrinterA") or build your own import lib for winspool.