RISC-V RV64GC GNU/Linux support

This patch series provide for a complete cross-build with default contrib configuration and with --disable-qt --disable-vdpau flags for the main VLC configuration.

Known issues:

• Video output is only supported via XCB (RENDER or plain X11), not tested:
  • Xlib and DRM are missing,
  • as well as Vulkan and OpenGL.
• GNU/Crypt and its reverse dependencies cannot be built due to the ancient libgpg-error version in contribs (#26506 (closed)).