fd leak when generating epiphany tarball

I'm trying to create a tarball release for Epiphany using BuildStream. I already have a workspace open for it. I follow these steps:

$ bst shell --build core/epiphany.bst
# mkdir build
# cd build
# meson ..
# ninja
# ninja dist

All goes fine until the final step, which fails horribly with a bunch of errors that look like this:

In file included from /usr/include/x86_64-linux-gnu/sys/types.h:215:0,
                 from /usr/include/glib-2.0/glib/deprecated/gthread.h:127,
                 from /usr/include/glib-2.0/glib.h:108,
                 from ../tmpr5g5wqli/epiphany-3.27.90/embed/../lib/ephy-debug.h:23,
                 from ../tmpr5g5wqli/epiphany-3.27.90/tests/ephy-gsb-service-test.c:23:
/usr/include/endian.h:61:11: fatal error: /usr/include/x86_64-linux-gnu/bits/uintn-identity.h: Too many open files
 # include <bits/uintn-identity.h>
           ^~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

I seem to have run out of file descriptors. Originally noticed in #227 (closed).