* build-aux/pre-inst-env.in (srcdir): Remove. (abs_top_srcdir, abs_top_builddir): Export. * lib/tests/posix/50-open-read.c (main): Use abs_top_srcdir.
* build-aux/test-c.sh: Support running by hand. * lib/tests/posix/50-open-read.c: New test. * lib/tests/posix/data/open-read: New file. * build-aux/check-mescc.sh (TESTS): Add it.