qemu: set localstatedir

Otherwise qemu-qa, qemu-pr-helper, and virtiofsd, try to write to
$out/var at runtime.

Fixes: https://github.com/NixOS/nixpkgs/issues/113909
Fixes: https://github.com/NixOS/nixpkgs/pull/112886

pkgs/applications/virtualization/qemu/default.nix

···
     })
   ];
 
+  # Otherwise tries to ensure /var/run exists.
+  postPatch = ''
+    sed -i "/install_subdir('run', install_dir: get_option('localstatedir'))/d" \
+        qga/meson.build
+  '';
+
   preConfigure = ''
     unset CPP # intereferes with dependency calculation
     # this script isn't marked as executable b/c it's indirectly used by meson. Needed to patch its shebang
···
       "--enable-docs"
       "--enable-tools"
       "--enable-guest-agent"
+      "--localstatedir=/var"
       "--sysconfdir=/etc"
     ]
     ++ optional numaSupport "--enable-numa"