9f7f5629c6
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.