Fix build with mingw-w64 headers.

	Fix build with mingw-w64 headers.
	* autoload.c: Define DECLSPEC_IMPORT for mingw-w64 headers.
	* filemanip.h: Include <sys/types.h> to fix missing mode_t typedef
	error with mingw-w64 headers.
	* gpg-packet.cc: Include "win32.h" to avoid macro redefinition
	errors with mingw-w64 headers.
	(ARRAYSIZE): Do not redefine.
	* main.cc (_argv): Declare if using mingw-w64 headers.
	(WinMain): Move up _argv definition to before it is first used.
	* ntdll.h: Include PSDK headers with mingw-w64 instead of DDK.
	* package_message.h: Include "win32.h" instead of <windows.h>.
	* propsheet.cc (PROPSHEETHEADER_V1_SIZE): Do not redefine.
	* win32.h: Include <sys/types.h> to fix missing mode_t typedef
	error with mingw-w64 headers.
	Define DECLSPEC_IMPORT for mingw-w64 headers.