feat: Mesa virgl DRI driver builds — virtio_gpu_dri.so (80MB pkgar)

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

Fixes:
- CFLAGS: -Dstatic_assert(...)= nullifies Linux-drm.h static_assert
  calls that conflict with Mesa util/macros.h redefinition on Redox
- virgl_screen.c: disk cache disabled for Redox (dl_iterate_phdr unavailable)
- bits/safamily-t.h: provided to cross-compiler toolchain sysroot

Build output:
- usr/lib/dri/virtio_gpu_dri.so — virgl DRI driver
- usr/lib/dri/swrast_dri.so — llvmpipe software renderer
- usr/lib/dri/kms_swrast_dri.so — KMS software renderer
- libEGL.so, libGLESv2.so, libgbm.so — with virgl support
- 80MB stage.pkgar (vs 63MB swrast-only)

This enables hardware-accelerated 3D rendering in QEMU via
-device virtio-vga-gl with virgl, using the virtio-gpu display
driver in redox-drm. The full stack for QEMU testing is now:

QEMU -device virtio-vga-gl
  → redox-drm virtio driver (KMS/GEM/pageflip)
  → Mesa virtio_gpu_dri.so (virgl gallium)
  → libEGL/libGLES2
  → Wayland compositor
  → KDE Plasma

recipes/libs/mesa/recipe.toml

@@ -3,7 +3,6 @@ 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 = [
@@ -47,7 +46,7 @@ cookbook_meson \
     -Dosmesa=true \
     -Dplatforms=redox \
     -Dshader-cache=disabled \
-    -Dc_args="['-Wno-error=implicit-function-declaration','-Wno-error']" \
+    -Dc_args="['-Wno-error=implicit-function-declaration','-Wno-error','-std=gnu11','-Dstatic_assert=_Static_assert']" \
     -Dcpp_args="['-Wno-error=implicit-function-declaration','-Wno-error']" \
     -Dvulkan-drivers=swrast \
     -Dshared-glapi=enabled