build: ensure build directory for generated sources exist
build: ensure build directory for generated sources exist

For out-of-tree builds, we must ensure that the build directory
for the generated sources exists. We do that by adding a dependency
to the .dirstamp file.

tklauser/libnl,dsahern/libnl,greearb/libnl-ct,thom311/libnl,dsahern/libnl,tklauser/libnl,thom311/libnl,dsahern/libnl,dsahern/libnl,greearb/libnl-ct,greearb/libnl-ct,tklauser/libnl,tklauser/libnl,thom311/libnl