Fix toolchain issue for windows build of libziparchive.

With mingw 4.8, the new default packed behavior is broken and makes
zip archive fails due to unexpected misalignment in
CentralDirectoryRecord.

This patch uses -mno-ms-bitfields to revert to the old packed
behavior.

Change-Id: Ic977c841e330e19451db1d31ddb22e570a525062