boot/arm: fix bootloader build issues without font and font_spleen

Change-Id: Ie9595f79de43bbb155c997bdbcf109e8e971e862
Signed-off-by: Han Pengfei <pengphei@qq.com>
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4086
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

src/system/boot/arch/arm/Jamfile

@@ -22,6 +22,8 @@ local kernelArchSources =
 
 local kernelDebugSources =
 	blue_screen.cpp
+	font.cpp
+	font_spleen.cpp
 	frame_buffer_console.cpp
 ;