add ninja-build prerequisite to qemu build

#142

Author: cirosantilli

build

@@ -352,7 +352,10 @@ so looping over all of them would waste time.
             'qemu': _Component(
                 self._build_file('build-qemu'),
                 apt_build_deps={'qemu'},
-                apt_get_pkgs={'libsdl2-dev'},
+                apt_get_pkgs={
+                    'libsdl2-dev',
+                    'ninja-build',
+                },
                 submodules={'qemu'},
             ),
             'qemu-baremetal': _Component(dependencies=[