crtl gaps surfaced by the undeclared-identifier warning: rmdir, F_OK/W_OK/R_OK, register

• Type: bug cluster (crtl completeness + one cfront keyword gap) — Track B (lib/crtl) for rmdir + the access() constants; Track C (cfront) for the register keyword.
• Status: done
• Found / Opened: 2026-07-10, immediately after the undeclared-identifier warning landed ([[bug-a-libcfree-unresolved-extern-silent-zero]], commit afa42ddd) — building sqlite now prints these instead of silently emitting 0.

Findings (all currently silent nulls / wrong values)

1. rmdir — same null-call class as pread. lib/crtl has no C rmdir wrapper, though the PAL already provides PalRmdir/PalBackendRmdir (unlinkat + AT_REMOVEDIR). sqlite references it; today it decays to a 0 slot. Fix: add __pxx_rmdir (pxxcio.pas → PalRmdir) and a rmdir() C wrapper in lib/crtl/src/unistd.c, prototype in unistd.h — mirror the ftruncate/access set added in commit d65d95d8.

2. F_OK / W_OK / R_OK / (X_OK) undefined. The access() mode constants are not defined by the crtl (fcntl.h/unistd.h), so access(path, F_OK) passes mode 0 by accident — wrong, and only "works" because F_OK==0. Define them (F_OK 0, X_OK 1, W_OK 2, R_OK 4) in the crtl header that declares access.

3. register reaches the value path. The C storage-class keyword register is not modelled by cfront, so it falls through to the identifier/value path and warns. Harmless at runtime (it's a no-op qualifier) but it should be consumed as a storage-class specifier in the declarator parser, like static/const/volatile. Track C.

Acceptance

• Building sqlite (and the crtl guards) emits no undeclared identifier warnings for rmdir, F_OK, W_OK, R_OK, or register.
• rmdir round-trips libc-free (mkdir a dir, rmdir it, stat → ENOENT); add to the b238-style crtl POSIX-IO guard.
• c-testsuite still 220/220; self-host byte-identical.

Log

• 2026-07-10 — resolved, commit 3d440574.