Factoring out README-release, now that it's in gnulib, using gnulib's new tight-scope rule and removing our use of its now-removed exit module:
[PATCH 1/4] maint: don't use now-removed gnulib "exit" module [PATCH 2/4] maint: prepare for the tight-scope check [PATCH 3/4] build: update gnulib submodule to latest [PATCH 4/4] maint: use gnulib's new readme-release module
