When compiling sys-libs/tdb[-python] PYTHON_SINGLE_TARGET is required to be set * No Python implementation selected for the build. Please set * the PYTHON_SINGLE_TARGET variable in your make.conf to one * of the following values: * * python2_6 python2_7
Seems very similar to #475370.
Fixed in https://gitweb.gentoo.org/repo/gentoo.git/commit/sys-libs/tdb?id=68d510080396b8c5c6d285aaf596210770cf7e14.