Arch Linux

Since QEMU 2.12 SDL2 and GTK3 are built by default as loadable run-time modules so /usr/bin/qemu-system-x86_64 is not link against those libs but the optionally loadable /usr/lib/qemu/*so are.

SDL2 UI (ui-sdl.so) needs libSDL2
GTK UI (ui-gtk.so) needs both libvte and libSDL2
SDL2 audio device (audio-sdl.so) needs libSDL2

Confirm with both ldd and running qemu with -display flag:
* as sdl: while vte3 was removed to confirm it's only needed for the gtk output
* as none: while sdl2 was removed to confirm qemu can without libsdl.

I suggest moving vte3 and sdl2 to optdepends:
* vte3: GTK UI support
* sdl2: SDL2 and GTK UI support, SDL2 audio device

libpulse can probably also be moved to optdepends as only audio-pa.so is linked against it but I didn't test if qemu runs without the lib correctly.

Changelog: https://wiki.qemu.org/ChangeLog/2.12

Default build config:
GTK: https://github.com/qemu/qemu/blob/v4.0.0/configure#L6770
and commit: https://github.com/qemu/qemu/commit/e0fb129c2f2baac0ef44408751bada8739f99522
SDL: https://github.com/qemu/qemu/blob/v4.0.0/configure#L6652
and commit: https://github.com/qemu/qemu/commit/96400a148b3e1337e2c451e95bc3c3c69a05b67c
SDL and PA audio: https://github.com/qemu/qemu/blob/v4.0.0/configure#L6594
and commits:
https://github.com/qemu/qemu/commit/051c7d5c1e2f4a392a4b89027b27aa4c50c16fe0
https://github.com/qemu/qemu/commit/d2f623dad5566dcfc3a85666d88c59124b280c95