Currently ebuild doesn't allow to enable fasteap feature together with openssl. I've modified ebuild, and wpa_supplicant builds cleanly with both fasteap and ssl flags set. Is there any reason for such limitation? I didn't manage to find lot info about it. It looks like earlier version of openssl were missing some functionalities regarding TLS extenstions, so additional patch was needed. In openssl-1.0.2k this functionalities are provided in upstream sources.
See https://github.com/gentoo/gentoo/pull/5236
2.6-r5