Set the default value if one isn't provided. Test: `get_build_var DIST_DIR` after removing the default setting in envsetup.mk Change-Id: I0cb310fc65f7747c36de14608b61786ef6863fd1
Set the default value if one isn't provided. Test: `get_build_var DIST_DIR` after removing the default setting in envsetup.mk Change-Id: I0cb310fc65f7747c36de14608b61786ef6863fd1