all: remove object files when `make depend` fails, as a fallback

cosmo-all/Dockerfile

@@ -35,6 +35,7 @@ RUN --mount=type=cache,id=cosmo-build-all,target=/cosmopolitan/o,sharing=locked
 # FIXME: SIGSEGV: \
  && skip "o/$mode/third_party/python/Lib/test/test_ioctl.py.runs" \
 \
+ && { ./makeit MODE="$mode" depend || find o -name '*.o' -delete ;} \
  && ./makeit MODE="$mode" all \
 \
 # install the binaries somewhere so we can retrieve them without mounting cache: \