AFAIK the only working hardware encoders were NVENC on Linux and Windows and VideoToolbox on macOS. This is just about to change with an addition of a working vaEncoder (libva based hw encoder Intel/Linux) thanks to great efforts by Mean.
XVBA hw decoding support was Linux-only, probably never sufficiently working and became completely obsolete with the demise of the fglrx video driver for Radeon graphics cards.
Avidemux mingw cross-builds or any other builds include no AMD libraries and don't link agains any.
