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.

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 \