Similarly to build_ext we need ccan/config.h to be present for dso to
build. It was not the case and so pip install wendelin.core was failing:

    $ pip install wendelin.core-2.0a2.tar.gz
    Processing ./wendelin.core-2.0a2.tar.gz
      Installing build dependencies ... done
      Getting requirements to build wheel ... done
        Preparing wheel metadata ... done
    Collecting ZODB>=4
    ...
    Building wheels for collected packages: wendelin.core
      Building wheel for wendelin.core (PEP 517) ... error
      ERROR: Command errored out with exit status 1:
      ...
      running build_dso
      Building DSOs
      building 'wendelin.bigfile.libvirtmem' DSO as build/lib.linux-x86_64-2.7/wendelin/bigfile/liblibvirtmem.so
      creating build/temp.linux-x86_64-2.7
      creating build/temp.linux-x86_64-2.7/bigfile
      creating build/temp.linux-x86_64-2.7/lib
      x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -ffile-prefix-map=/build/python2.7-vgIf7a/python2.7-2.7.18=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -D_GNU_SOURCE -I/tmp/pip-build-env-lfVr7E/overlay/lib/python2.7/site-packages -I. -I./include -I./3rdparty/ccan -I./3rdparty/include -Ibuild/lib.linux-x86_64-2.7/. -c bigfile/pagefault.c -o build/temp.linux-x86_64-2.7/bigfile/pagefault.o -fno-strict-aliasing -std=gnu99 -fplan9-extensions -Wno-declaration-after-statement -Wno-error=declaration-after-statement
      In file included from ./include/wendelin/list.h:11,
                       from ./include/wendelin/bigfile/virtmem.h:50,
                       from bigfile/pagefault.c:29:
      ./3rdparty/ccan/ccan/array_size/array_size.h:4:10: fatal error: config.h: Нет такого файла или каталога
          4 | #include "config.h"
            |          ^~~~~~~~~~
      compilation terminated.
      error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
      ----------------------------------------
      ERROR: Failed building wheel for wendelin.core
    Failed to build wendelin.core
    ERROR: Could not build wheels for wendelin.core which use PEP 517 and cannot be installed directly

-> Fix it by making build_dso also first come through `make all`.

NOTE we cannot fix it in exactly the same way as for build_ext: if we split
build_dso into build_dso and ll_build_dso, `make all` will still go to infinite
recursion: build_dso -> ll_build_dso -> build_dso (not ll_build_dso, this is controlled by setuptools_dso) -> oops.