make menuconfig doesn't work!

Yikes! this can happen because cleaning all the package dependencies emerge --depclean removed all the kernel source code.

find out what kernel /usr/src/linux points to:

eamoc@knut ~ $ ls -l /usr/src/linux
lrwxrwxrwx 1 root root 20 May 28 00:28 /usr/src/linux -> linux-3.12.20-gentoo
then emerge the appropirate sources:

sudo emerge -av sys-kernel/gentoo-sources:3.12.20

Problem sorted