Fail to build on OS X

[abitrolly]

There is an error while building tdu for OS X.

# github.com/josephpaul0/tdu
./tdu.go:154:18: too many arguments in call to getTtyWidth
	have (*s_scan)
	want ()
./tdu.go:848:9: assignment mismatch: 2 variables but osInit returns 1 values
./tdu.go:867:7: too many arguments in call to osEnd
./tdu_generic.go:35:18: undefined: sc_scan

I've made a Homebrew package for tdu, and the error is reported by Homebrew CI - https://github.com/abitrolly/homebrew-tap/runs/3234326039#step:8:30

[josephpaul0]

Hello,
There is a regression for Mac OS X.
In tdu_generic.go
func getTtyWidth() int { return 80 }
should be replaced with :
func getTtyWidth(sc *s_scan) int { return 80 }

Several compilation errors seem to be triggered by the missing sc *s_scan
I will look into all errors and provide a patch.

Regards