Corrected various build problems

- Corrected return value on make_link on Windows
- Used _utime on Windows because utime is not defined on WDK
- Fixed warnings concerning time_t to double conversions (MSVC 2010)
- Avoid warnings on lfs_setmode for Unix
- Avoid redefining _O_TEXT and _O_BINARY (Cygwin)
- Moved content of pushresult into make_link, to avoid a warning (MinGW)