We were previously maintaining two lists of the child Makefile
fragments---one for the includes and another for the dependencies. So,
of course, they drifted and the dependency list wasn't up to date.
We fix this by adding a single subdirs variable, and then using GNU
Makefile substitution to generate both the include and the dependency
lists.
Some side effect of this change caused the '=' assignment of the dir
variable to not work anymore. I'm not sure why that is, but using ':='
makes sense here and fixes the problem.
Some compilers complain that result might be used uninitialized in
this function. I believe such compilers simply aren't looking hard
enough, but it's easy enough to silence them.
These were copied from the gnulib git repository as of:
commit 563c779682040ed4b89c9b4bbe428dcd8157c90a
They come under the GNU GPL v3 (or later) exactly as notmuch is
licensed.
