[pdftex] Minor compilations issues under Cygwin

[Olivier Lefevre]

1. Not robust agaisnt paths with embedded spaces.
    Specifically the call to config.sub in configure
    will fail and that seemed to be the issue
2. The call to strip at the end fails because the
    build infrastructure did not take into account
    the fact that Windows executables end in .exe

Regards,

-- O.L.