platforms/gentoo: form a single emerge command
platforms/gentoo: form a single emerge command

wkentaro/rosdep,sorki/rosdep,aymanim/rosdep,allenh1/rosdep,alessandro-aglietti/rosdep,ros-infrastructure/rosdep,alessandro-aglietti/rosdep,georgepar/rosdep,wkentaro/rosdep,spaghetti-/rosdep,allenh1/rosdep,georgepar/rosdep,ros-infrastructure/rosdep,aymanim/rosdep,sorki/rosdep,spaghetti-/rosdep