The proposed solution is in the tracker. If this is an autotools based package, and '--disable-silent-rules' doesn't work, you can try to add MAKEOPTS+=" V=1"
+ 22 Nov 2012; Rick Farina <zerochaos@gentoo.org> powertop-2.2.ebuild: + fix bug #444370 by switching to EAPI5, there goes my cherry