Gentoo Linux installation instructions
Gentoo comes with a gnuradio ebuild in the official package repository.
$ emerge gnuradio
Alternatively, you can install GNU Radio manually from source:
Gentoo Linux manual installation instructions
Firstly emerge the packages that GNU Radio depends on.
$ emerge swig fftw cppunit boost alsa-lib sdcc guile wxpython xmlto numpy gsl
cmake will tell you if something is missing.
Configuring using cmake
The regular cmake build chain should work. You might have to set the QWT path manually.