Fix qemu command to not warn about raw disk image file

Rsconscript

@@ -34,5 +34,5 @@ uefi_env = env "uefi" do |env|
 end
 
 task "run" do
-	sh %W[qemu-system-x86_64 -bios OVMF.fd -hda #{uefi_env.expand("^/efi-loader.img")}]
+	sh %W[qemu-system-x86_64 -bios OVMF.fd -drive file=#{uefi_env.expand("^/efi-loader.img")},format=raw]
 end

src/main.d

@@ -9,6 +9,8 @@ void write_string(EFI_SYSTEM_TABLE * st, const(wchar)[] str)
 
 extern (C) EFI_STATUS efi_main(EFI_HANDLE image_handle, EFI_SYSTEM_TABLE * st)
 {
+    st.ConOut.ClearScreen(st.ConOut);
+
     write_string(st, "Hello, D UEFI world!\r\n"w);
     write_string(st, "Press any key...\r\n"w);