While running the test suite ("make check") on the latest emacs sources, I
got this error:

  CCLD     data/emacs-module/mod-test.so
In file included from
../../../src/emacs-2019-10-17/test/data/emacs-module/mod-test.c:20:
../src/config.h:2257:10: fatal error: conf_post.h: No such file or directory
 2257 | #include <conf_post.h>

conf_post.h does exist in $(srcdir), but I'm building in a separate
directory.

Please let me know if you need more details.

Thank you,
  Vin Shelton