Improve multiproduct_kati output

It now uses the same output style as ninja, overwriting status lines in
smart terminals.

Test: multiproduct_kati
Test: multiproduct_kati | cat
Change-Id: I8db5198ffdc5ebc5503241ac492379753d92978e
diff --git a/ui/build/context.go b/ui/build/context.go
index f85bb6c..52a337d 100644
--- a/ui/build/context.go
+++ b/ui/build/context.go
@@ -102,3 +102,7 @@
 	}
 	return false
 }
+
+func (c ContextImpl) TermWidth() (int, bool) {
+	return termWidth(c.Stdout())
+}