sdl3: keep SDL3_test from linking against libunwind

SDL3's CheckLibUnwind cmake macro autodetects libunwind for the
SDL3_test library and offers no option to disable it. On the buildbots
libunwind is present in staging, so the test programs end up linked
against it and packaging libsdl3-tests fails:

  Package libsdl3-tests is missing dependencies for the following libraries:
  libunwind-x86_64.so.8
  libunwind.so.8

This aborts the whole sdl3 build before anything is staged, taking
down every package depending on SDL3 or SDL2 (sdl2-compat, sdl2-image,
sdl2-mixer, sdl3-image, sdl3-mixer, sdl3-doom, gzdoom, vice).

Preseed the three detection cache variables to OFF so the result no
longer depends on whether libunwind happens to be staged; it is only
used for symbolised backtraces in test leak reports.

Fixes: 51549dadd5 ("sdl3: add SDL3 3.4.10")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

libs/sdl3/Makefile

@@ -2,7 +2,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=sdl3
 PKG_VERSION:=3.4.10
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=SDL3-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://github.com/libsdl-org/SDL/releases/download/release-$(PKG_VERSION)/
@@ -66,7 +66,10 @@ CMAKE_OPTIONS += \
 	-DSDL_WAYLAND=ON \
 	-DSDL_WAYLAND_LIBDECOR=OFF \
 	-DSDL_WAYLAND_SHARED=ON \
-	-DSDL_X11=OFF
+	-DSDL_X11=OFF \
+	-DLIBC_HAS_WORKING_LIBUNWIND=OFF \
+	-DLIBUNWIND_HAS_WORKINGLIBUNWIND=OFF \
+	-DPC_LIBUNWIND_HAS_WORKING_LIBUNWIND=OFF
 
 define Package/libsdl3
   SECTION:=libs