Iceprog progress counter stutters when run under apio/scons on windows

[zapta]

When running apio upload on windows with the iceprog programmer, the progress counter is not updated smoothly as it done when running iceprog using apio raw -- iceprog .... The reason is that the scons output pipes are buffered with 4K buffer size despite the fact we set it to be unbuffered. The problem was on observed in windows only and is OK on linux and macOS.

I am not sure how that can be fixed but creating this issue anyway.

[zapta]

Update: it seems that the problem is that the progress bar output from iceprog, which is terminated with \r is not flushed out after each write which causes the output for be buffered under some conditions. Adding an explicit flush command fixes the issue.

[zapta]

Created an upstream iceprog issue YosysHQ/icestorm#350 and PR YosysHQ/icestorm#351

Upgrade Apio's oss-cad-suite package to the latest oss-cad-suite version once that PR is accepted.