Add a GnuTests workflow that, on push and PR, fetches the GNU grep release
tarball, builds the Rust grep binary, runs util/run-gnu-testsuite.sh, and
uploads the JSON results. An aggregate job compares the run against the
reference summary from the default branch (util/compare_test_results.py,
borrowed from ../sed) and fails only on new, non-intermittent regressions;
known-flaky tests are listed in .github/workflows/ignore-intermittent.txt.
Add util/fetch-gnu.sh (downloads the GNU grep 3.12 release tarball from
ftp.gnu.org) and util/run-gnu-testsuite.sh, which reuses the gnulib test
framework shipped in the tarball (tests/init.sh + init.cfg) and injects the
Rust grep binary via PATH, replicating tests/Makefile.am's TESTS_ENVIRONMENT.
Each test is classified by its gnulib exit code (0=PASS, 77=SKIP, else FAIL)
and results are emitted as JSON.
Modelled on ../sed (lightweight PATH-injection runner) and ../coreutils
(release-tarball fetch). Current baseline: 61 pass / 39 fail / 28 skip of 128
tests -- the failures quantify the remaining GNU-compatibility gap.
Sylvestre Ledru