sdl2: build without libunwind

[dangowrt]

SDL2 links tests against libunwind if libunwind is detected by CMake. This results in build failure due to undefined symbols. Prevent building with libunwind for now.

[Ansuel]

@dangowrt should we disable test instead? Test are run on host machine right?

[dangowrt]

Test are run on host machine right?

No, tests are built for the target system and are installable as libsdl2-tests package. The installed executables can be used e.g. to verify that audio, video or input drivers are working fine on the target, some are also useful as benchmark.

[Ansuel]

Ok so problem is that they are linking to the wrong library? aka host library are leaking? Just trying to understand the compile error without having to build the monster ahahah

[dangowrt]

Looks like src/test/SDL_test_memory.c uses symbols defined in libunwind.h but not actually present without linking with -lunwind, which is probably due to SDL2 use of the CMake build system. After all, this leads to linker error:

/builder/shared-workdir/build/sdk/staging_dir/toolchain-aarch64_cortex-a53_gcc-13.3.0_musl/bin/../lib/gcc/aarch64-openwrt-linux-musl/13.3.0/../../../../aarch64-openwrt-linux-musl/bin/ld.bfd: libSDL2_test.a(SDL_test_memory.c.o): in function `ret173':
SDL_test_memory.c:(.text+0x1a0): undefined reference to `_ULaarch64_init_local'
/builder/shared-workdir/build/sdk/staging_dir/toolchain-aarch64_cortex-a53_gcc-13.3.0_musl/bin/../lib/gcc/aarch64-openwrt-linux-musl/13.3.0/../../../../aarch64-openwrt-linux-musl/bin/ld.bfd: SDL_test_memory.c:(.text+0x1a8): undefined reference to `_ULaarch64_step'
/builder/shared-workdir/build/sdk/staging_dir/toolchain-aarch64_cortex-a53_gcc-13.3.0_musl/bin/../lib/gcc/aarch64-openwrt-linux-musl/13.3.0/../../../../aarch64-openwrt-linux-musl/bin/ld.bfd: SDL_test_memory.c:(.text+0x1c0): undefined reference to `_ULaarch64_get_reg'
/builder/shared-workdir/build/sdk/staging_dir/toolchain-aarch64_cortex-a53_gcc-13.3.0_musl/bin/../lib/gcc/aarch64-openwrt-linux-musl/13.3.0/../../../../aarch64-openwrt-linux-musl/bin/ld.bfd: SDL_test_memory.c:(.text+0x1dc): undefined reference to `_ULaarch64_get_proc_name'

See https://downloads.openwrt.org/snapshots/faillogs/aarch64_cortex-a53/video/sdl2/compile.txt

As libunwind is only used for one test, and even there only provides optional additional information, the easiest way is to just build without libunwind even if it is present in staging_dir/hostpkg.

[dangowrt]

Sadly Github CI is not very useful for those larger build jobs. Only the logs of the successful builds are part of the log archive and trying to view "raw logs" of the failed builds ends up truncated, so it's impossible to tell why it failed. Buildbots are going to tell once merged (if at all failing on the buildbots)...