Remove use of .libs for Windows build.

Under Windows the package should be configured to disable shared
library build.
Detect unseekable files and don't try to seek.

The previous functionality used the fallback behavior when a call
to fseek() failed, but under Windows the seek can partially succeed
even if a failure occurs. Use ftell() to detect when the input is
unseekable and then always use the fallback behavior.
Don't run symlink tests on Windows.
Add unlha32.dll -lhx- test archives.
Add decoder for unlha32.dll -lhx- format.

Thanks to Multi for providing the patch.