Packing a file w/ PACK_EFFORT=0 (no compression) is really slow for
large files (> 1MB can take few mns to few hours).
The problem is amplified on windows when using mounted disks over
a samba server.

This is due to unbuffered output of javax.pack.Pack200.pack API
in PACK_EFFORT=0 case, only.

PACK_EFFORT=0 is mainly used internally, for example by RE to produce
jcov builds.