android - Ant rebuilding library projects every time -

i have android project includes 2 android library projects.

i'm using command ant debug build project , takes around 1min , 20sec. i've counted 17 seconds used compile first android library project , 42 seconds used compile second android library project.

since these 2 dependency projects updated it's not necessary compile them each time.

how can avoid ant compiling 2 android library projects each build?

add dont.do.deps=1 local.properties (or pass property ant other way)