common: unset CMAKE_GENERATOR before sourcing templates

When building dependencies of packages this has to be unset to avoid
using e.g. CMAKE_GENERATOR="Unix Makefiles" for a package which expected
to build with the default of make_cmd=ninja, and would subsequently fail
with "ninja: error: loading 'build.ninja': No such file or directory"
during do_build() if do_configure() generated a Makefile instead of a
build.ninja file.

common/environment/setup/sourcepkg.sh

@@ -8,6 +8,7 @@ unset -v configure_script configure_args wrksrc build_wrksrc create_wrksrc
 unset -v make_build_args make_check_args make_install_args
 unset -v make_build_target make_check_target make_install_target
 unset -v make_cmd meson_cmd gem_cmd fetch_cmd make_check_pre
+unset -v CMAKE_GENERATOR
 unset -v python_version stackage
 unset -v cmake_builddir meson_builddir
 unset -v meson_crossfile