"make dist" did not depend on $(BUILT_SOURCES)
* lib/am/distdir.am (distdir-am): New intermediate target.
Interpose this target between $(distdir) and its dependency
on $(DISTFILES), so that we can ensure $(BUILT_SOURCES) are
all created before we begin creating $(DISTFILES).
* t/dist-vs-built-sources.sh: Test for this.
* t/list-of-tests.mk (handwritten_TESTS): Add it.
* NEWS (Bugs fixed): Mention it.
Assaf Gordon reported that "make dist" (after ./configure
from a pristine clone of GNU hello) would fail due to the
absence of configmake.h while compiling lib/localcharset.c.
https://lists.gnu.org/r/bug-hello/2014-03/msg00016.html