feat: Mesa virgl gallium driver — hardware-accelerated 3D for QEMU

Mesa now builds with -Dgallium-drivers=swrast,virgl for Redox target.

Fixes:
- virgl_screen.c: wrapped disk cache creation in #ifndef __redox__
  (build_id_find_nhdr_for_addr uses dl_iterate_phdr — unavailable on Redox)
- bits/safamily-t.h: provided to cross-compiler toolchain sysroot

Durable patch:
- local/patches/mesa/P4-virgl-redox-disk-cache.patch (25 lines)

This enables hardware-accelerated 3D rendering in QEMU via
virtio-gpu + virgl. Mesa EGL/GLES2/GBM now support the virgl
gallium driver alongside llvmpipe software renderer.

63MB pkgar artifact with virgl support.

local/patches/mesa/P4-virgl-redox-disk-cache.patch

@@ -0,0 +1,25 @@
+diff --git a/src/gallium/drivers/virgl/virgl_screen.c b/src/gallium/drivers/virgl/virgl_screen.c
+index d86ca5d1e..f79b8c678 100644
+--- a/src/gallium/drivers/virgl/virgl_screen.c
++++ b/src/gallium/drivers/virgl/virgl_screen.c
+@@ -1054,6 +1054,12 @@ static struct disk_cache *virgl_get_disk_shader_cache (struct pipe_screen *pscre
+ 
+ static void virgl_disk_cache_create(struct virgl_screen *screen)
+ {
++#ifdef __redox__
++   (void)screen;
++   /* build_id_find_nhdr_for_addr uses dl_iterate_phdr — not available on Redox.
++    * Disk cache is disabled; shader compilation works without it. */
++   screen->disk_cache = NULL;
++#else
+    const struct build_id_note *note =
+       build_id_find_nhdr_for_addr(virgl_disk_cache_create);
+    assert(note);
+@@ -1078,6 +1084,7 @@ static void virgl_disk_cache_create(struct virgl_screen *screen)
+    _mesa_sha1_format(timestamp, sha1);
+ 
+    screen->disk_cache = disk_cache_create("virgl", timestamp, 0);
++#endif
+ }
+ 
+ static bool

recipes/libs/mesa/recipe.toml

@@ -3,6 +3,7 @@ git = "https://gitlab.redox-os.org/redox-os/mesa.git"
 upstream = "https://gitlab.freedesktop.org/mesa/mesa"
 branch = "redox-24.0"
 shallow_clone = true
+patches = ["../../../local/patches/mesa/P4-virgl-redox-disk-cache.patch"]
 [build]
 template = "custom"
 dependencies = [
@@ -41,7 +42,7 @@ cookbook_meson \
     -Degl=enabled \
     -Dgbm=enabled \
     -Dglx=disabled \
-    -Dgallium-drivers=swrast \
+    -Dgallium-drivers=swrast,virgl \
     -Dllvm=enabled \
     -Dosmesa=true \
     -Dplatforms=redox \