Add support for COFF bigobj format

[ahomescu]

On x64 Windows, object files are stored in COFF format by default, but that puts a limit on the number of sections in the file (NumberOfSections is a 16-bit WORD in the header). Microsoft added another header format that uses DWORDs for both the number of sections and symbol, in the form of the ANON_OBJECT_HEADER_BIGOBJ structure in winnt.h. We may need to add support for it at some point in the future.