On Windows, don't generate "mt" command when CRT is statically
linked. [Jan Dubois]On Cygwin, examine $Config{useshrplib} to see whether we're
supposed to be linking with a shared perl library or not. [Reini
Urban]In link_executable() on Cygwin, trust $Config{ld} rather than using
$Config{cc} for linking. [Reini Urban]Add 'haiku' as a Unix-like platform. [Ingo Weinhold]