Install dependencies on Gentoo

Install the GMT dependencies with:

# Install required dependencies
emerge sci-libs/netcdf net-misc/curl sci-libs/gdal

# Install optional dependencies
emerge app-text/ghostscript-gpl

# to enable movie-making
emerge media-gfx/graphicsmagick media-video/ffmpeg

# to enable document viewing via gmt docs
emerge x11-misc/xdg-utils